To provide a reduction gear which does not cause leakage of lubricating oil.

A pair of holding plates 26 are provided at the end part of an output shaft carrier 6 along the peripheral direction at intervals which correspond to specified angle of rotation of the output shaft carrier 6, and a pair of stopper bolts 27 for abutting on the holding plates 26 respectively to suppress the rotation of the output shaft carrier 6, are provided on the outside face of a gear case 11. Since the range of rotation of the output shaft carrier 6 is limited by the holding plates 26 and the stopper bolts 27 outside the gear case 11, the need for stopper mounting holes penetrating the gear casing 11 is eliminated.