Pivot arm supported by a base is pivotable about an arm support shaft by being pulled via a throttle cable, and a throttle cam supported by the base via a cam support shaft and having a guide groove that has a guide section of the pivot arm movably therein. The arm support shaft and the cam support shaft are disposed in non-parallel relation to a valve shaft of the throttle valve and at such positions as not to overlap the throttle valve as viewed from a lateral side of the throttle valve drive mechanism.