A first concave-convex portion of a first transmission member is engaged with an intermediate concave-convex portion of an intermediate transmission member with a circumferential gap being therebetween. A second concave-convex portion of a second transmission member is engaged with the intermediate concave-convex portion with a circumferential gap being therebetween. A first elastic member and a second elastic member are engaged with a first engagement portion and a second engagement portion of the intermediate transmission member such that separation between the intermediate transmission member and the first elastic member and the second elastic member can be prevented.