Share trading on the Tokyo stock market was suspended for more than four hours on Tuesday after a computer fault.
Traders had to sit on their hands for more than four hours
The Tokyo Stock Exchange, the world's second largest market, had to delay share trading after an upgrade to its software system caused a breakdown.
Market analysts said the problem could hinder the exchange's plans to float its own shares next year.
Despite the suspension, the Nikkei 225 benchmark index rallied in a truncated session, closing up 1.9% at 13,867.86.
Share trading on Tuesday only began at 1.30pm Japanese time, four and half hours later than usual.
The stock market had upgraded the software used to process transactions last month in an effort to handle record levels of dealing.
Trading has been buoyant this year as Japan's economic fortunes have continued to improve, with the Nikkei hitting a four-year high.
The delay to the start of the session - which also curtailed trading in bonds for much of the day - was the first since 1997.
The stock exchange said it "deeply apologized" for the problem while Kaoru Yosano, minister for economic and fiscal policy, described the situation as "regrettable".
"I hope the exchange will immediately investigate why the failure occurred and take measures to ensure this does not happen again," Mr Yosano said.
The problem is an embarrassment for the exchange as it is seeking to attract investors for a planned flotation of its own shares next year.
The company which oversees the market plans to become the second publicly traded stock exchange in Japan after the Osaka Securities Exchange floated in March.
One analyst described the glitch as "unbelievable".
"The Tokyo Stock Exchange should be grateful that they aren't listed yet," Yoshihiko Kosuga, deputy general manager at Mizuho Investors Securities, told Reuters.
"The problem would have been bigger if they were public."
The forced suspension of trading on any of the world's largest stock markets is rare.
In 2000, the London Stock Exchange delayed the start of trading due to a software glitch which led to incorrect price information being displayed.
The New York Stock Exchange cut trading short by four minutes earlier this year due to an IT problem.