The record was achieved even after the 225-index's heavyweight SoftBank Group rose by almost ten percent.
At lunchtime, the index had risen by 1.0 percent, while the broader Topix index increased by 0.2 percent.
However, the biggest rise is for Shenzhen's composite index, which climbs 2.2 percent. Shanghai's equivalent rose by 0.9 percent.
On the other hand, Hong Kong's Hang Seng index fell by 0.5 percent.
