Abe and Aso have come under fresh pressure over the ministry's admission this week that it had altered documents related to the sale of state-owned land at a steep discount to a school operator with ties to Abe's wife, Akie.
Suspicion of a cover-up could slash Abe's ratings and dash his hopes for a third term as leader of his Liberal Democratic Party (LDP). Victory in the LDP September leadership vote would put him on track to become Japan's longest-serving premier.
Copies of documents released by the finance ministry on Monday showed that references to Abe, his wife and Aso were removed from the ministry's records of the sale to school operator Moritomo Gakuen.
"When you look at the documents even before they were altered, it is clear that my wife and I were not involved," Abe told an upper house budget committee on Wednesday.
Abe has said he would resign if evidence were found that they had.
According to the ministry documents, a comment from Moritomo Gakuen citing Akie Abe as telling him, "This is good land so please proceed," was removed. Yasunori Kagoike, the former head of Moritomo Gakuen, and his wife remain in custody after being arrested last July over the deal.
Asked about the reference on Wednesday, Abe said: "I checked with my wife and she says she said no such thing. My wife was neither the person in charge of establishing the school nor Mr Kagoike's boss, so naturally she would not have made such a remark."
Abe and Aso told parliament they had never instructed officials at the finance ministry to alter the documents.
