A heat treatment apparatus includes a furnace body, a door, and a pipe. The furnace body has therein a processing space where the workpiece is heat-treated, and it is provided with an opening. The door closes the opening of the furnace body. A refrigerant flows through the pipe. The door is provided with a seal material in a region that overlaps a peripheral edge of the opening of the furnace body when the door is closed. The pipe is attached around a region in the furnace body against which the seal material is pressed.