Back in the 1990s, Mitsui Fudosan Co. 8801.TO +2.46% was one of the few Japanese real-estate companies that stuck with its U.S. investments and didn't retreat with big losses when that market collapsed.

Now Mitsui, which has $40 billion of property on its books, is once again going against the grain. Many Japanese real-estate companies are only just starting to emerge onto the international stage after years of focusing on Asia. But Mitsui is pursuing risky deals in the U.S. and Europe.

Mitsui's ambition and appetite for risk are reflected in a series of developments in New York, Los Angeles and London, including a 42-story luxury apartment block in midtown Manhattan and the soon-to-be-vacated home of the British Broadcasting Corp. in London.

And Mitsui has no intention of applying the brakes. The Japanese developer and manager has its sights set on Paris as a launch pad for European expansion, according to the head of the firm's business in Europe. The company has set aside a $5 billion war chest for investment outside Japan by 2017.

"The scale and liquidity in Paris is good, and the timing might be right," says Hideto Yamada, Mitsui Fudosan's managing director in Europe.

Mitsui has a larger appetite for global risk than many other Japanese real-estate companies, partly because, unlike others, it didn't abandon these markets in the 1990s. Its decision to remain behind gave the company the expertise and confidence to continue making investments in the U.S. and the U.K.

So far, many of these bets have paid off. The company's shares have climbed more than 160% in the past 12 months. But some of the investments Mitsui is making today could run into trouble if the European economic crisis worsens or the U.S. recovery stalls.

Consider the 177,000-square-foot office building in London's financial district that Mitsui is planning to develop with Stanhope PLC. The project is in preconstruction, with a completion target of late 2014. In December, a tentative lease with Miller Insurance Services LLP for space in the project was shelved.

Currently, Japanese investors are minor players in real estate outside Asia, according to Jones Lang LaSalle JLL -0.13% . In 2012, they spent only $396 million in the Americas and $787 million in Europe, along with $19.7 billion in the Asia-Pacific region, Jones Lang says.

Only now are Japanese investors returning to international markets. "We are now seeing a resurgence of Japanese interest in direct real-estate investment," says Matthew Richards, head of Jones Lang's international capital group in Europe.

Mitsui joined other Japanese companies in a buying binge of U.S. real estate during the 1980s, which was fueled by a rapidly expanding home economy and global expansion of Japanese business. Among other properties, Mitsui purchased the 2.3-million-square-foot tower at 1251 Avenue of the Americas in Manhattan.

That binge ended abruptly as the Japanese asset bubble burst in the late 1980s, causing most firms to shed their properties and retreat to Japan. In one high-profile loss, Mitubishi Estate Co. was forced to put the storied Rockefeller Center complex in New York into a bankruptcy proceeding.

Mitsui retained its ownership of the Avenue of the Americas building through the downturn and even invested millions in renovation. Today, the building is the most valuable property Mitsui owns. "We came to be very confident and comfortable when investing" when others stopped, says Mr. Yamada.

Mitsui's goal is to reduce the proportion of its home-market assets to 70% of its total portfolio, from about 90% currently. Although Japan is showing signs of an economic revival after years of low growth, Mitsui says there are limited opportunities for investment in assets of the size and scale to meet its ambitions. The group also wants to diversify its risk profile by spreading its investments.

In the U.S., Mitsui is moving forward with a rental-apartment building development at 160 Madison Ave. in New York. The 300-unit project, which is slated to start this summer and finish in the fall of 2015, is in partnership with DLJ Real Estate Capital Partners.

Meanwhile, in London, projects include a £85 million ($131.8 million) office development on Moorgate, one of the main thoroughfares in London's financial district. That 132,000-square-foot project is set to be completed in early 2014. Also, Mitsui last year bought a 45% stake in the BBC television center in West London, the 1.1 million-square-foot home of the public broadcaster, for about £95 million. The company plans to turn the studios into a mixed office, retail and residential site when the BBC moves out in 2015.

Mr. Yamada says Mitsui wants to invest "in similar scale opportunities" in continental Europe. He singles out Paris and Stockholm as areas of interest and says developments would likely be made in partnership with a local operator.

Mitsui has tried to break into continental Europe before, unsuccessfully. In the 1990s, the group signaled its intention to invest but failed to find a suitable target as recession swept the continent in the early part of the decade.

Although difficult economic conditions still exist in much of Europe, Mr. Yamada says Mitsui will be bolder this time. "Our vision at the highest corporate level is different," he says. "Now, we need to expand to keep the speed of our growth."