To provide a clutch mechanism of a small rotary machine that is used for usage in which torque is required from the starting time of the rotary machine.

The clutch mechanism K, which comprises a guide plate 13, on which a first guide surface 16 is provided on both protruding portions 22 on both sides of a recessed part 15; a weight 17, which is arranged movably inside the recessed part 15 and on both sides in the movement direction of which second guide surfaces 18 are formed; and lock members 19 provided in contact with the first and second guide surfaces 16, 18 and an output shaft casing 11, is incorporated between a rotor casing 9 and the output shaft casing 11 connected to an output shaft 5 provided coaxially at the outside circumference side of the rotor casing 9.