To improve lubrication operation at the bearing of the rotary shaft of a gear.

A side plate 7a and an annular sealant 10 having approximate the same thickness as that of a 3-shaped sealant 9a are disposed in a gap between a front cover and a rear cover in a manner to surround a slide part between shafts 5a and 5b and a bearing. Oil leaking through a gap between the shafts 5a and 5b and the side plate 7a toward the bearing is guided to a slide part between the shafts 5a and 5b and the bearing and lubrication operation is improved.