That marks a steep drop from more than 50% in the 1980s, underscoring how far Japan's market structure has shifted away from entrenched corporate tie-ups.
Yamaji presented the change as part of Tokyo's stock-market revival, arguing Japan has spent decades building financial infrastructure that could help it withstand a sharp Wall Street correction.
The remarks come as investors weigh risks from still-rising US stocks, higher rates and inflation, and a prolonged US-Israel war against Iran.