He also said that his wife, Wu Shu-chen, had wired $20 million to a bank account in Switzerland. Taiwanese media reports said that Wu told prosecutors that the money included unspent donations.
Chen quit his Democratic Progressive Party (DPP) on Friday after Liu Chao-shiuan, Taiwan's president, confirmed that an investigation had been launched into the money laundering allegations.
"I have to say sorry to DPP members and supporters with a heavy heart. I let everybody down and caused irreparable damage to the party. This was not my intention but I made mistakes," he said in a statement.
"To show my deepest remorse, my wife Wu Shu-chen and I leave the DPP from now," he said.
The Taiwanese investigation follows a similar move by Swiss authorities.
Shih Ming-teh, a former leader of the DPP, said on Sunday that the $20m sent to Switzerland could be the tip of the iceberg.
He accused Chen of taking at least $85m from an entrepreneur bidding for bank ownership during a spate of mergers initiated by the government in 2005.
Copies of Swiss documents obtained by Hung Hsiu-chu, a Kuomintang MP, showed that Chen's son and daughter-in-law had transferred $31m into her Swiss bank accounts in 2007.
The couple left Taiwan on August 9 before the case came to light, according to Taiwanese authorities.
A string of corruption scandals implicating Chen, his family and another senior DPP officials have tarnished the party's image and played a part in its defeat in a presidential vote in March.
Chen was already under investigation for allegedly embezzling $480,500 in special expenses from the government while he was president, and his wife is on trial for corruption and document forgery in the same case.