Terunobu Maeda, president of Mizuho Holdings Inc., told the Diet on Tuesday that the banking group acknowledges its grave responsibility for computer glitches that have led to depositors being double billed and ATMs malfunctioning.

Speaking before a House of Representatives committee, where he was summoned as an unsworn witness, Maeda again apologized for the 2.5 million cases in which depositors were unable to move their money.

The problems began April 1, when the world's biggest financial group was launched.