A substrate includes a first surface portion, which covers a heat receiving portion of a radiation member together with a resinous member. The substrate further includes a second surface portion, which is on the outer periphery of the first surface portion. The substrate makes contact with the resinous member via the second surface portion. The first surface portion and the heat receiving portion have a first contact boundary therebetween. The second surface portion and the resinous member have a second contact boundary that surrounds the first contact boundary. The second contact boundary is sealed using a sealing member. The sealing member is restricted from flowing into a boundary between the first contact boundary and the second contact boundary.