A protruding portion 100 having a sloped surface 100b sloped against a ceiling surface is provided on the ceiling side of a cooking chamber 20. Superheated steam from a steam temperature-raising device 50 is blown off from first ceiling steam blowoff openings 101 provided in a flat surface 100a of the protruding portion 100 toward a bottom face within the cooking chamber 20, while the superheated steam is blown off from second ceiling steam blowoff openings 102 provided in a sloped surface 100b of the protruding portion 100 toward the side face within the cooking chamber 20. The superheated steam blown off from these steam blowoff openings 101 and 102 is effectively supplied to upper-and-back surface of a heating object 90 rested in the cooking chamber 20 so as to be spaced from the bottom face of the cooking chamber 20.