A riding lawn mower having a front mower unit, comprises a plurality of wheels; a vehicle body supported by the wheels; an engine supported by the vehicle body for driving at least one of the wheels; a lift link supported by the vehicle body; a mower unit adapted to be disposed forwardly of the vehicle body, having at least one cutting blade, and supported to be pivotable about an axis of a first pivot pin relative to the lift link between a generally horizontal position wherein the at least one cutting blade faces the ground, and a generally vertical position wherein the at least one cutting blade is oriented forward; an assisting force exerting device for exerting an assisting force for moving the mower unit to the generally vertical position; a support link connected to an end of the assisting force exerting device, wherein the assisting force exerting device and the support link are disposed between the lift link and the mower unit; a fixing member having a first position for permitting the assisting force from the assisting force exerting device to be transmitted to the mower unit by releasably engaging the support link with the lift link and the mower unit, and a second position for prohibiting the assisting force from the assisting force exerting device from being transmitted to the mower unit by disengaging the support link from the lift link and the mower unit.