An underseat structure of a road vehicle which protects an occupant from engine heat while enhancing the maintenance property of a vehicle which includes an engine supported on a vehicle body frame, and an engine oil supply pipe and an oil level gauge mounted on the engine, wherein the engine is disposed below at least one seat. An inner cover is disposed between the at least one seat and the engine and a maintenance lid is provided for allowing maintenance of the engine oil supply pipe and the oil level gauge formed on the inner cover with the inner cover being detachably mounted on the vehicle body frame.