An image reading apparatus includes a substrate, a light guiding member, an image reading portion, and a supporting member. The light guiding member has a first contact surface and a second contact surface. The supporting member has a third contact surface supporting the first contact surface and a fourth contact surface supporting the second contact surface. In a cross section crossing the longitudinal direction, at least one of the first contact surface of the light guiding member and the third contact surface of the supporting member is a curved surface. In the cross section crossing the longitudinal direction, at least one of the second contact surface of the light guiding member and the fourth contact surface of the supporting member is a curved surface.