PURPOSE: To freely set a power transmission channel by linking element speed reducers together through a first and a second linked mechanism which can be linked together under the state of permitting inclination between a rotation axis of one of the speed reducers and a sun gear of the other speed reducer, and mutually between fixed cases of one and the other speed reducers.

CONSTITUTION: A spherical gear 211 is formed on the end of a rotation axis 171, and a U-shaped section recessed groove 222 having inner teeth where the end of the rotation axis 171 fits, is provided on the right end surface of a sun gear 152 which constitutes an adjoining element speed reducer 112. For this reason, the directions of the rotation axes 171, 172 of one of the element speed reducer 111 and the other element speed reducer 112 become changeable within the range of about 20° whereby constituting a first linked mechanism 30 of the mutually adjoining element speed reducers 111, 112 which can be linked together in an inclined state of a specified angle. A second linked mechanism 40, which can link the speed reducers 111, 112 together in a state of permitting inclination in a specified angle, is also constituted by means of a protrusion 181 on a fixed case 131 and a recessed groove 192 on a fixed case 132.