PURPOSE: To provide shaft fitting structure preventing both shafts from being decentered at the time of connecting a driven shaft and a rotation output driving shaft to each other.

CONSTITUTION: Shaft fitting structure is constituted of a holder part 88 and a clamp 91. The clamp 91 has arm parts 91a, 91b formed in such a way as to hold a driven shaft 6. These arm parts 91a, 91b are overlapped in the crossed state at the respective upper and lower parts, and screws are provided between the respective erected parts. When the driven shaft is inserted into the shaft fitting structure, the screws provided at the upper and lower parts of the respective overlapped arms are fastened in the well balanced state. The driven shaft is thereby fastened and fixed to the center in the shaft fitting structure.