A photoelectric sensor includes: a light projecting section projecting detection medium light to a detection object region; and a light receiving section receiving reflecting light or transmitted light from the detection object region, the sections being in a single piece or in separate pieces. The optical surfaces are composed of matched conics of rotation. The evaporator extends over at least part of the wall pertaining to the lower region, and the cooling performance of the evaporator, in its part pertaining to the upper or lower region, is such that the temperature reached in the upper region of the inner chamber is lower than that reached in the lower region. A disc assembly includes a plurality of rotatable discs carried by the splined surface of the shaft, a plurality of stationary discs which alternate with the rotatable discs and a primary stationary disc located at the end of the disc assembly, proximate to the open end of housing. , the first polishing where polishing is stopped on the surface of the barrier metal film 219 and the second polishing where the remaining barrier metal film 219 and the tapered sacrificial film 213 are polished.