Actuator includes a lock mechanism for locking the actuator against movement in one end position, and a separate lock release assembly exteriorly mounted on the side of the actuator housing. The lock release assembly includes a toggle linkage directly engageable with the movable lock part to disengage the lock when a suitable force is applied to the toggle linkage exteriorly of the actuator. A lock spring is located immediately between the movable lock part and actuator piston for resetting the lock as the actuator nears such one end position.