An intake air control device in which a valve shaft extending in the left and right direction of a vehicle body frame across an air intake path formed in an air intake path forming body is rotatably supported by the air intake path forming body connected to a cylinder head of an engine body which is to be mounted to the vehicle body frame of a saddle type vehicle, and a butterfly-shaped throttle valve is fixed to the valve shaft so as to control the opening of the air intake path, the intake air control device further comprising: an actuator connected to one end of the valve shaft and including an electric motor which can drive the valve shaft to rotate; a throttle opening sensor connected to the one end of the valve shaft for detecting a rotational position of the valve shaft; and a throttle operating amount sensor mounted to a supporting frame for detecting the amount of turning operation of a throttle drum which rotates in response to the throttle operation by the vehicle operator when a vehicle operator turns a throttle grip mounted to a steering handle of the saddle type vehicle, characterized in that the throttle drum is mounted to the other end of the valve shaft so as to be capable of relative rotation, and the throttle operating amount sensor is supported by the air intake path forming body so as to oppose the throttle drum while being connected to the throttle drum; and the throttle operating amount sensor includes a detection shaft projecting toward the throttle drum coaxially with the valve shaft and a detection arm extending radially of the detection shaft fixed to a distal end portion of the detection shaft, and wherein an engaging arm having a pair of engaging portions (40a, 40a) for sandwiching the distal end portion of the detection arm from both sides along the circumference of the valve shaft is secured to the throttle drum at a position offset from the axial line of the valve shaft. an actuator connected to one end of the valve shaft and including an electric motor which can drive the valve shaft to rotate; a throttle opening sensor connected to the one end of the valve shaft for detecting a rotational position of the valve shaft; and a throttle operating amount sensor mounted to a supporting frame for detecting the amount of turning operation of a throttle drum which rotates in response to the throttle operation by the vehicle operator when a vehicle operator turns a throttle grip mounted to a steering handle of the saddle type vehicle, characterized in that the throttle drum is mounted to the other end of the valve shaft so as to be capable of relative rotation, and the throttle operating amount sensor is supported by the air intake path forming body so as to oppose the throttle drum while being connected to the throttle drum; and the throttle operating amount sensor includes a detection shaft projecting toward the throttle drum coaxially with the valve shaft and a detection arm extending radially of the detection shaft fixed to a distal end portion of the detection shaft, and wherein an engaging arm having a pair of engaging portions (40a, 40a) for sandwiching the distal end portion of the detection arm from both sides along the circumference of the valve shaft is secured to the throttle drum at a position offset from the axial line of the valve shaft.