To provide an actuator position sensor connected to a hydraulic circuit for sensing the position of an actuator by sensing the flow of a working oil supplied to the actuator.

The actuator position sensor 9 is equipped with an oil passage 10H, a pair of gears 13 and 14 installed on the way of the oil passage 10H, meshed with each other and supported rotatably and rotating with the working oil flowing through the passage 10H, and rotation sensors 15 and 16 to sense the rotations of the gears. The gears 13 and 14 rotate with the working oil flowing through the oil passage 10H, and the sensors 15 and 16 sense the rotations of the gears 13 and 14 and emit signals. The direction of the working oil flowing through the passage 10H, i.e., the rotating directions of the gears 13 and 14, can be sensed on the basis of the phase shift between the signals from the sensors 15 and 16, and the position of the actuator (stroke) connected to the oil passage 10H can be sensed by counting the teeth of the gears 13 and 14 rotating.