Saikawa said he would return the money. He told reporters that an internal company investigation found that he had received the money.
"I thought everything was being carried out properly, and I didn't know anything," Saikawa told reporters.
Nissan Motor Co. said that the findings from its ongoing internal investigation will be reported to the board of directors Monday, but declined to elaborate, saying the board was independent.
"We have heard that share appreciation rights will also be part of this report," the company said, referring to the payments linked to Nissan share prices that executives, including Saikawa, received as bonuses.
Japanese media reports have said that the dates were changed to allow the maximum amount of cashing in on the stock prices, allowing Saikawa to receive tens of millions of yen (hundreds of thousands of dollars) in dubious compensation.
The latest development comes as former Nissan Chairman Carlos Ghosn is awaiting trial on charges of falsifying documents on deferred compensation and of breach of trust in allegedly diverting Nissan money for personal gain. He denies wrongdoing.
Saikawa blamed what he called "the Ghosn system" at Nissan for the payments, and said the system was being reviewed.
Saikawa succeeded Ghosn and in the past was closely allied with Ghosn, who led Nissan for two decades and made it one of the most successful automakers in the world.
Saikawa said he had left the task of overseeing the compensation system to Greg Kelly, a former board director who was arrested last year with Ghosn on financial misconduct allegations. Kelly has maintained he is innocent.
Since the arrests of Ghosn and Kelly, Nissan profits and sales have tumbled. Investors are also worried about Nissan's relationship with alliance partner Renault SA of France, which owns 43 percent of Nissan. Ghosn was sent in by Renault to lead Nissan, and in the years before his arrest had led both Renault and Nissan.
The Associated Press contributed to this report.