To provide a small joint preventing idle running of an output shaft.

The joint 4 for coupling the output shaft 2 and a driven shaft 3 comprises: a columnar projection 44 fitted in a columnar hole 21 arranged at a tip of the output shaft 2 and formed at a shaft center; and a flat projection 46 which has a flat part 45 arranged at the tip of the output shaft 2, formed at a position recessed to the shaft center side from a shaft outer peripheral surface, and brought into pressure contact with a plane 22 parallel to an axial direction, and which is formed to a height more than an axial direction height of the columnar projection 44.