A heater includes a heating member formed in a plate shape that includes a substrate-heating surface on which a substrate is mounted and a heating member rear surface which is on the opposite side of the substrate-heating surfaces. The heater also has a resistance heating element embedded therein. An auxiliary member is placed on the side of the heating member rear surface of the heating member and has an opposing surface which opposes the heating member rear surface. A planar gas path for gas ejected on the substrate-heating surface is formed between the heating member rear surface and the opposing surface.