A safety lever (safety control member) is provided in its inner surface with first, second and third positioning holes. The tapered outer end part of a safety lock (trigger blocking member) is engaged in the first positioning hole of the safety lever to retain the safety lever at a perfect lock position. In this state, the forward turning of the upper arm of the trigger is blocked by the safety lock. Thus, the trigger cannot turn even if the same is pulled. Since the safety lock is fitted in a sliding hole formed in a casing so as to be slidable in directions perpendicular to a plane in which the trigger turns, and force applied to the trigger is born by the casing, the safety lock does not deform and is able to block the movement of the trigger with reliability even if the trigger is pulled strongly. In this state where the safety lever is at the perfect lock position, the bolt blocking part of the safety lever is engaged in a groove formed in a bolt. In this state, the bolt is locked perfectly and cannot be turned to open the chamber. When the safety lever is turned to a safety position, the bolt can be operated, while the trigger is still restrained from turning by the trigger blocking part of the safety lock.