Heat treatment apparatus and heat treatment method

When a semiconductor wafer does not exist in a chamber, a halogen lamp is lighted. Light emitted from the halogen lamp successively transmits a lower chamber window and an upper chamber window of a quartz and is received by a spectrophotometer. The spectrophotometer measures spectrum intensity of the transmitted light. A determination unit determines whether or not the lower chamber window and the upper chamber window are contaminated by comparing the measured spectrum intensity of the transmitted light with a reference intensity in a case there is no contamination. Another spectrophotometer monitors time degradation of the halogen lamp.