A heat treatment apparatus is configured to include: a treatment chamber for accommodating therein a wafer; a substrate supporting unit for horizontally supporting the wafer in the treatment chamber; and a lamp unit provided above the treatment chamber. The lamp unit includes: a base member; a plurality of lamps provided on the lower surface of the base member whose front ends face downwardly; a plurality of ring-shaped reflectors concentrically provided on the lower surface of the base member to protrude downward; and a cooling head for supplying a cooling medium into the reflectors. At least some of the lamps are arranged along the reflectors, and cooling medium channels, each inner space of which is formed as a ring-shaped space, are respectively provided within the reflectors in the extending directions of the reflectors.