Abstract: A motion reducing device, adapted to be attached to the frame of and driven by an electric motor, includes a rigid disk provided with a planar toothed ring portion which is meshed with a sector of a toothed ring portion of a flexible disk radially secured to the driven shaft. The pitch of the ring portion is slightly different from that of the planar toothed ring portion. The driving shaft is coaxial with the driven shaft and has radially secured to it another disk parallel to the rigid disk and carrying a roller which causes sequentially a sector of the toothed ring portion to yield in a direction parallel to the common axis thereby driving the other shaft. The device is housed in a sealed lubricant containing cylindrical box having an integral bottom secured to the frame of the motor and through which passes the motor shaft, the box being closed at the opposite end by the above mentioned rigid disk.