Abstract: A gear device includes a gear, a pin, a plate member, a retainer portion, a contact part and a non-contact part. The pin is inserted into an opening of the gear. The plate member is disposed on a face of the gear and attached along an outer peripheral surface of the pin. The retainer portion is disposed in a vicinity of an end portion of the pin, with the plate member being interposed between the retainer portion and the face of the gear. The contact part is formed by faced surfaces of the retainer portion and the plate member with parts of the faced surfaces annularly making contact in a position closest to an outer peripheral surface of the pin. The non-contact part is formed by the faced surfaces with parts of the faced surfaces not making contact in a position away from the outer peripheral surface of the pin.