PURPOSE: To correct the stop position, minimize the size, lighten the weight and increase output of the rotary type air cylinder in a rotary type air cylinder by converting torque of a vane by supplied compressed air to thrust or tensile force of a cylinder output rod through a hammer blow structure formed of an output side claw, a screw and a nut.

CONSTITUTION: This air cylinder is constituted of an air motor 10, a hammer blow structure 40 and an output rod unit 50. This air motor 10 is formed of a vane 13, and rotation of the rotor 12 is decelerated in a planetary gear structure consisting of a coaxial first solar gear 20 and transmitted to a motor output shaft 29. Subsequently, the hammer blow structure 40 is formed of a shaft units 42, 44 spring 46 of input output side claws 41, 43, and a cylinder output rod 55 is slid by a screw shaft 51, a screw nut 53 and a locking groove 56 fixed on the shaft unit 44 of the output side claw 43 of the output rod unit 50. Consequently, it is possible to take a correct stop position and to increase output with this air cylinder of small size and light weight.