An actuator-operation detecting apparatus is configured to check the operating state of a piston of an actuator. The actuator includes a double-acting cylinder, the piston that partitions the cylinder into a first pressure acting chamber and a second pressure acting chamber, and a rod connected to an end face of the piston facing the second pressure acting chamber. The actuator-operation detecting apparatus includes a first pressure detector to detect the pressure in the first pressure acting chamber, a second pressure detector to detect the pressure in the second pressure acting chamber, a differential amplifier circuit to calculate a thrust force acting on the piston based on the pressures detected by the first and second pressure detectors and the pressure-receiving area of the piston, and a microcomputer to monitor the operation of the piston based on the thrust force.