To provide a device capable of reducing friction between gears for a small external force generated in a pressed gear and, in generation of a large external force, absorbing the external force.
A transmission mechanism 50 transmitting a rotational force of an electric motor 40 driven according to a relative angle of rotation between an input shaft 21 rotating interlocking with rotation of a handle and an output shaft 22 rotating interlocking with the direction of a wheel, to the output shaft 22 includes: a driving gear 51 mounted on a rotary shaft of the electric motor 40; a driven gear 52 mounted on the output shaft 22; an intermediate gear 53 interposed between the driving gear 51 and the driven gear 52; and a coil spring group 60 pressing a tooth surface of the intermediate gear 53 against tooth surfaces of other gears. When the axial displacement amount of the intermediate gear 53 is less than a predetermined amount, the pressing force of the coil spring group 60 increases by a predetermined increase amount or less according to the displacement amount, while when the displacement amount is equal to or larger than the predetermined amount, the pressing force increases over the predetermined increase amount.
MIYAZAKI MASANOBU
SHINBO HIROSHI
Fumio Ogata
Takeshi Senda