SPEED REDUCTION MECHANISM AND MOTOR ROTATIONAL FORCE TRANSMISSION DEVICE INCLUDING THE SAME

PROBLEM TO BE SOLVED: To provide a speed reduction mechanism capable of suppressing generation of inclination and movements of a rotary shaft and a motor rotational force transmission device including the speed reduction mechanism.SOLUTION: A speed reduction transmission mechanism 5 comprises: a ball bearing 44 rotatably supporting a motor shaft 42 on an inner peripheral surface of a second housing element 21; a ball bearing 38 which is disposed in parallel with the axial direction on a differential case 30 side of the ball bearing 44 and rotatably supports a flange 30f of the differential case 30 on an outer peripheral surface of the motor shaft 42; and a ball bearing 67 which is disposed on the radial direction outside of the ball bearing 38 and rotatably supports the flange 30f on an inner peripheral surface of a rotation power application member 52. Each of the ball bearings 38 and 67 receives an axial load P=P,Pas a pre-load while the ball bearing 44 receives an axial load P=Pas a pre-load.