A first heating element and a second heating element, which are capable of individually controlling temperatures thereof, are embedded in a ceramic base. Each of the first heating element and the second heating element is formed into a spiral shape so as not to contact the other from a central portion of the base to an outer circumferential portion thereof in substantially the same plane parallel to a heating surface of the base. One of the first and second heating elements includes a high heating density portion on the central portion side of the base, and a low heating density portion on the peripheral portion side of the base, and the other of the first and second heating elements includes a low heating density portion on the central portion side of the base, and a high heating density portion on the peripheral portion side of the base.