A parallel glass which is a prism having a parallelogram-shaped cross section in an x-y direction, and parallel glasses which are prisms having a parallelogram-shaped cross section in the x-y direction and each include grooves formed in one surface in a z direction perpendicular to the x-y direction, are stacked in direct contact with each other such that the grooves are located on the inside, and light trying to enter the grooves is subjected is total reflection, thereby changing incident parallel beams with a pitch of 13 mm into emergent parallel beams with a pitch of 1 mm.