PURPOSE: To reduce or dissolve the resonance of a deflector caused by the vibration of a rotary shaft by extending the end part of a deflector, fixed to the outer periphery of a case in a place where a rotary shaft is inserted, toward the periphery of a companion flange so as to cover the flange peripheral surface with a specified gap.

CONSTITUTION: A bearing retainer for holding a bearing 15 supporting a rear output shaft 14 is fixed to the outside of a case 10. The end part 52 of a deflector 50, fixed to the end part periphery of the bearing retainer 40, is extended toward the outer periphery 42b of a companion flange 42 so as to cover this outer periphery 42b with a specified gap. Since this deflector 50 is fixed to the bearing retainer 40 side forming a part of the case 10, chain contact vibration is not directly transmitted to the deflector 50. The deflector 50 is thereby prevented from receiving such chain contact vibration as to reach the natural resonance frequency, and this results in preventing the generation of noise caused by the resonance of the deflector 50.