Bases (4, 5), i.e., two or more layers of board-like members having different expansion coefficients, are stacked on an upper section of a Peltier element (2) disposed on a bottom section of a case (20), a suppressing member (22) having an expansion coefficient different from that of the base (5) on the topmost layer is further provided at least on a part of a region of the base (5) of the topmost layer, and an optical element is disposed on the base (5) and/or the suppressing member (22). Thus, even when the Peltier element (2) is about to warp, since generation of warpage is suppressed by the plyboard structure composed of the base (4), the base (5) and the suppressing member (22), the base (4) and the suppressing member (22) do not easily warp and an optical axis shift between a beam splitter (8) and an etalon (9) is not easily generated.