A concentrator photovoltaic unit being an optical system base unit includes: a concentrating portion configured to converge sunlight; a cell configured to receive light converged by the concentrating portion to generate power; a package including a frame portion, the frame portion having insulating property and surrounding the cell, the package being in integrated relation with the cell; a shield plate provided between the concentrating portion and the cell, and including an opening allowing light converged by the concentrating portion to selectively pass therethrough; and a protection plate being a heat-resistant member provided on the frame portion to make the cell expose to the light and to shield the package, the protection plate being in contact with nothing but the frame portion, and securing a predetermined insulation distance from a live portion of the cell.