An electrostatic chuck is provided, having an insulation layer including a mount plane on which a wafer is mounted, an inner electrode provided in the insulation layer, and projecting portions protruding from the mount plane which include contact planes that contact the wafer. A backside gas flows into a space defined by the mount plane, the projecting portions, and the wafer under such a condition that the wafer is attracted to the mount plane so as to maintain the temperature uniformity of the wafer. The total areas of the contact planes of the projecting portions is not less than 5% and not more than 10% with respect to the area of the inner electrode, and the heights of the projecting portions are not less than 5 &mgr;m and not more than 10 &mgr;m.