A lock device (1) attached to a casing (15) of a fluid pressure rotary actuator (10) to lock a rotating shaft (11) of the rotary actuator (10). The lock device (1) has a sleeve (14) fitted to an end of the rotating shaft (11), a case body (2) having a key-type opening, a coil spring (7) placed in the case body (2) so as to fasten the outer periphery of the sleeve (14), and unlocking actuator (8) for unlocking the lock. A cover plate (3) is fitted to the rear surface of the case body (2).
