PURPOSE: To enhance the surface accuracy of a wall with simple working, and to facilitate the assembling of pinion gears, and also to enhance the positioning accuracy by carrying out the positioning of each one end of a pair of pinion gears by the wall of the housing hole formed in the case cover.

CONSTITUTION: A pair of side gears 15, 17 and a plurality of pairs of pinion gears 35, 37 are rotatably arranged inside a case 3 for receiving a rotational input, and the respective pairs of pinion gears 35, 37 are engaged with each other, and the side gear 15 on one side is engagedly connected to a driving shaft on one side, and the side gear 17 on the other side is connected to a driving shaft on the other side. In this case, as for the pinion gear 35, a first gear part 39 and a second gear part 41 are fitted in the housing hole 43a on the side of a case body 11, and in the housing hole 43b on the side of a case cover 13 respectively; and the left end thereof is positioned by the wall 43c on the side of the case cover 13, while the right end thereof is positioned by the wall 43d on the side of the case body 11. The pinion gear 37 is fitted in a housing hole 45, and both the ends thereof are positioned by respective walls 45c and 45d.