Provided is a planar heater in which a carbon wire heat generator is housed in along quartz glass housing portion, and the planar heater suppresses disconnection of the carbon wire heat generator by limiting a contact region between the carbon wire heat generator and the long housing portion, and capable of efficient radiation heating. In the planar heater, the plurality of long housing portions is disposed on the same plane, and heat is generated by energizing the carbon wire heat generator, each of the plurality of long housing portions is formed in a polygonal circular arc shape in which a plurality of linear portions is connected at a bent portion, respectively, and the plurality of long housing portions is disposed along the circumferences of a plurality of concentric circles.