A gear device includes a first gear, and a second gear meshing with the first gear. At least the first gear is made of a resin. The gear device further includes a connection member connected to an external member, a path member disposed in a path leading to the first gear and the connection member, and other members that are members other than the first gear, the second gear, the connection member, and the path member, and are made of a resin. The first gear, the connection member, and the path member are made of a resin having a higher thermal conductivity than a thermal conductivity of the other members.