To provide a joint structure of a rotary shaft capable of joining a rotary shaft without applying excessive force, and being lightly rotated even when the centers of a rotor and a shaft are slightly disagreed with each other, or the rotor is slightly inclined.

This joint structure has a projecting side joint 31 having a cylindrical part, a recessed side joint 30 comprising a circular space part 16c capable of freely fitting the cylindrical part 19, at least one projection 22 formed in the direction crossing a rotary shaft of the projecting side joint, a groove 16d formed on the recessed side joint and enabling the projection to be entered therein, and a ring-shaped member 21 mounted on an outer periphery of the cylindrical part and having a toroidal-shaped outer peripheral surface, and the toroidal-shaped outer peripheral surface of the ring member is slidably contacted with an inner peripheral surface of the circular space part 16c. As a shaft 19 as the cylindrical part is oscillatable, the disagreement of the center of the hole 16c with that of the shaft 19 can be absorbed by the oscillation, even when the disagreement exists.