PURPOSE: To produce a motor gear efficiently in a short term by combining individually produced motors and gear units arbitrarily thereby attaching an auxiliary rotary unit such as a pulse encoder.

CONSTITUTION: A motor gear comprises a motor 1 coupled through flanges with a gear unit 4, a coupling shaft 11 having one end coupled through a cylindrical part 9 with the rotary shaft 3 of the motor and the other end coupled with the input shaft 10 of the gear unit 4, and an auxiliary rotary unit (20 or 30) for the motor. Rotary section 21 of the auxiliary rotary unit is fixed to the coupling shaft and the fixed section 22 of the auxiliary rotary unit is fixed to a fixed member interposed between the gear unit and the motor. Cylindrical part of the coupling shaft and the input shaft are supported by the fixed member through bearings, as required, and the auxiliary rotary unit is disposed between the bearings. According to the constitution, the motor gear can be accomplished in block-build system for different motor protection system with short overall length.