In a heat treatment apparatus, a substrate held by a holding part is irradiated with light emitted from halogen lamps to perform preheating thereon and irradiated with a flash of light emitted from flash lamps to perform flash heating thereon. Part of light which is emitted from the halogen lamps and goes toward the flash lamps passes through a window hole formed in a peripheral-light shielding member and enters the substrate held by the holding part, and its energy is used for the preheating on the substrate. On the other hand, the remaining light is blocked out by the peripheral-light shielding member.