To provide a heat treatment device that utilizes a catalyst activation heater for heat treatment, and suppresses increase in size and costs of the device.

This heat treatment device 1A includes a heat treatment furnace 20 for housing a workpiece W, an air conditioning section 23 provided with the heater 32 and a blower 33, and a heat insulating chamber 2 having communication passages 24, 25 for connecting the heat treatment furnace 20 and the air conditioning section 23. The heat treatment device 1A includes a recirculation path 5 and a catalyst 6. The recirculation path 5 is constituted to return the air flowing out from the air conditioning section 23 to a part upstream of the location of the heater 32 in the air conditioning section 23. The catalyst 6 decomposes the sublimate generated from the workpiece W in heat treatment of the workpiece W. The catalyst 6 is disposed at a part downstream of the location of the heater 32 in the air conditioning section 23.