Abe, who swept to power in late 2012 on a ticket to revive the economy, told parliament he "didn't know" that two firms had given money to the Liberal Democratic Party within a year of receiving government subsidies -- a violation of strict political funding laws.
The comments followed reports today in the Tokyo Shimbun and conservative Sankei newspaper, which said the chemical companies gave a combined 620,000 yen (USD 5,200) to a local party office in Abe's constituency in 2012 and 2013.
Japan's political funding laws ban firms from making a donation within a year of being notified that they will receive public money. But the legislation also says politicians must know about the subsidies, which Abe denies.
Last week the prime minister's farm minister Koya Nishikawa quit over accusations that he accepted illegal political funds, in a first blow to Abe's new cabinet which took office in December.
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Nishikawa has admitted receiving a one million yen donation from a company run by a sugar manufacturers' group months after the farm ministry decided to grant a 1.3 billion yen subsidy to the group.
In Abe's previous cabinet, two female ministers resigned last year over allegations that they had misspent money in what opponents insisted was an attempt to buy votes.
Money scandals are not uncommon in Japan, where pork barrel politics reigns and rules on spending tend to be slightly opaque -- barring little except explicit bribery and vote-buying.