"We're mindful that excessive declines in super-long bond yields, such as those with maturity of 20 years, could hurt public sentiment and economic activity by lowering the interest life insurers and pension funds earn from their investment," BOJ Executive Director Eiji Maeda told parliament.

"But the current ultra-loose monetary environment is stimulating the economy by spurring capital expenditure and housing investment. That will push up household income and asset prices," he said.

(Reporting by Leika Kihara; Editing by Chang-Ran Kim)