The Pokemon franchise creator surged nearly 11 percent to end the morning at 30,780 yen ($290), up more than 100 percent from its July 6 close.
That put Nintendo’s market capitalisation at 4.36 trillion yen, topping Sony, one of Japan’s best-known companies by 300 billion yen.
On Friday, Nintendo set a record for the most shares ever traded daily in Japan.
Since its launch two weeks ago, the game for mobile gadgets has been a surprise hit and sparked a worldwide frenzy among users who have taken to the streets with their smartphones.
The free app uses smartphone satellite location, graphics and camera capabilities to overlay cartoon monsters on real world settings, challenging players to capture and train the creatures for battles.
Investors are betting its popularity is a good sign for Nintendo’s nascent push into mobile gaming, a major U-turn for a company that long insisted on a consoles-only policy.
The Pokemon craze has also boosted other stocks in Tokyo. McDonald’s Japan — which has been struggling to get past a series of food safety scandals — soared as much as 23 percent in the morning after it started on Friday giving away with Happy meals figurines based on the game’s characters such as Pikachu.
It ended the morning up 9.37 percent at 3,325 yen.
“Investors are flocking to Pokemon-related stocks and McDonald’s Japan is one of those benefiting from the boom,” said Mitsushige Akino, executive officer at Ichiyoshi Asset Management.
“The boom came at a time when McDonald’s business has already started recovering and there’s expectation that the Pokemon toy offering will further increase customer traffic to their shops.”
The game was first launched in the United States, Australia and New Zealand. Since the weekend it has been released in more than two dozen more countries, but it has yet to be released in Japan.
Nintendo declined to say when the app would be released in its home market, and Niantic — which developed the game for Nintendo — did not reply to requests for comment.
Forbes cited Niantic chief executive John Hanke as saying the reason for the delay is that Japan’s server capacity is not powerful enough to keep up with expected demand.