A heating device 1 includes a flat heating chamber 3 provided with a side opening. A substrate W is carried in a horizontal position through the side opening into the processing chamber 3, and is subjected to a heating process in the heating chamber 3. the heating chamber 3 is provided with heating plates 34 and 35 respectively provided with heating elements 34a and 35a, and a cooling mechanism 2 for cooling the heating plates 34 and 35. A controller 7 controls the cooling mechanism such that the heating plates 34 and 35 are cooled after the completion of the heating process for heating the substrate W and before a succeeding substrate W is carried into the heating chamber 3, and controls the heating elements 34a and 35a such that the heating plates 34 and 35 are heated at a processing temperature after the succeeding substrate has been carried into the heating chamber 3.