A riding mower includes a pair of right and left front wheels; a pair of right and left rear wheels; a driver's seat provided between the rear wheels and the front wheels; an engine provided in the rear of the driver's seat; and a mower provided under the driver's seat. The riding mower is capable of being mounted with a fuel gas cylinder sideways on a side of the engine in which an operation section of the fuel gas cylinder faces backward. The riding mower further includes a guard member that is opposed to a rear surface of the fuel gas cylinder and is switchable between a protection position to cover the rear side of the operation section and an open position to open the rear surface of the fuel gas cylinder.