A substrate processing apparatus includes a heating unit that heats a processing chamber that processes a plurality of substrates and that quickly cools the processing chamber after the processing. The heating unit includes a body having an intake port and an exhaust port, one or more heaters located inside the body, a cooler connected to the intake port of the body, an exhaust pump connected to the exhaust port of the body, and a controller controlling the cooler. The substrate processing apparatus includes a boat in which a plurality of substrates are stacked, a processing chamber providing a space in which the substrates are processed, a transfer unit carrying the boat into or out of the processing chamber, and the heating unit located outside the processing chamber.