To reduce temperature difference produced on a wafer surface by difference of temperature rise velocity between a wafer and a mounting stand of the wafer, and restrain generation of slip when annealing treatment, for example, is carried out by heating a semiconductor wafer by using a heat radiant lamp.

A wafer is mounted on an annular mounting stand which supports a wafer from a circumferential edge lower side in a treatment container and is heated by a number of heat radiant lamps opposite to a wafer. A quartz light transmitting window is provided between a wafer and a heat radiant lamp, an upper side of a circumferential edge of the light transmitting window is flat, and a convex lens which projects to a treatment space side is formed in a lower side thereof. Among beams emitted from a heat radiant lamp, beam toward an outside of a mounting stand is deflected at a convex lens and gets together inside. Therefore, a temperature rise velocity of a mounting stand increases by the amount, thus reducing temperature difference between a wafer and a mounting stand during temperature rise.