in a speed reduction motor comprising a motor and a speed reduction device connected to the motor for the purpose of reducing and transmitting rotation therethrough , a gear casing for housing gears of the speed reduction device is formed integrally with a rear gear bracket and a stator frame , so that the number of working steps are reduced and alignment of the gears is enhanced with high accuracy . further , an opening portion is provided on an outer circumference of the gear casing through which the gears can be installed with ease of assembly .