A medical manipulator includes an actuator block having a motor, a coupler detachably mounted on the actuator block and having a rotor connected to a rotatable shaft of the motor, a distal-end working unit mounted on a distal end of a joint shaft, which extends from the coupler and is operatively connected to the rotor by a wire, an encoder for detecting an angular displacement of the motor, and a controller for reading a signal from the encoder and comparing the read signal with an operation command value for energizing the motor through a feedback loop. The controller outputs a signal having a level greater than the resolution of the encoder and a lower operation limit of the motor within a range in which the distal-end working unit remains still, and monitors the angular displacement of the motor for thereby determining whether the feedback loop is malfunctioning or not.