A rod integrator holder 6 has concave clearance grooves 67A to 67D elongated in the direction of the optical axis L, at the corners within a case 61 thereof. The clearance grooves 67A to 67D are configured such that the edges 84A to 84D of the rod integrator 8 can be prevented from coming into contact with the inner faces 66A to 66D of the case 61. The edges 84A to 84D of the rod integrator can be prevented from being broken by coming into contact with the inner faces 66A to 66D of the case 61, and the edges 84A to 84D of the rod integrator 8 and the inner faces 66A to 66D of the case 61 can be prevented from rubbing against each other to generate dust due to abrasion.