A heat treatment device includes: a heating chamber inside which a treatment object is contained; a lower heater that heats the lower section of a receiving area that is an area inside the heating chamber in which the treatment object is contained; and an upper heater that heats the upper section of the receiving area.

A refill system includes a tempering furnace, a refill furnace which stores the molten potassium nitrate obtained by melting powdered potassium nitrate, a supply unit which supplies the molten potassium nitrate to the tempering furnace, a tempering furnace side load measuring unit which measures a load amount of the molten potassium nitrate in the tempering furnace, a refill furnace side load measuring unit which measures a load amount of the molten potassium nitrate in the refill furnace, and a central control unit which checks the load amount of the molten potassium nitrate in the tempering furnace and the refill furnace in real time, and controls the supply unit to stop supplying the molten potassium nitrate to the tempering furnace when the load amount of the molten potassium nitrate in the tempering furnace is greater than or equal to a predetermined load amount.