Abe and his aides have repeatedly denied intervening to help Kake Educational Institute win approval for a veterinary school in a special economic zone.
The approval raises doubt because the institution's director, Kotaro Kake, is a friend of Abe. Suspicions swirled when a former official testified there was "instruction from the highest level" for him to help Kake.
Several opinion polls show Abe's support dipping below 30 percent, the lowest since he took office in 2012.
