Abstract: A rear underside structure of a vehicle as a rear undercover main body, an air flow path, an air intake opening, and an air exhaust opening. The rear undercover main body has an inclined planar part that rises toward the rear of the vehicle, and is disposed further to the rear of than the fuel tank, between the front and rear axles, so as to cover a drive element of the vehicle. The air flow path is disposed between the rear undercover main body and the drive element. The inclined planar part delineates at least a rear part of the air flow path. The air intake opening is disposed further to the front than the drive element, and the air exhaust opening is disposed to the rear of the inclined planar part. Air which flows in from the air intake opening passes through the air flow path, and is exhausted from the exhaust opening.