To provide a plane heater, including a carbon wire heating element CW, in which surface arrangement density of the heating element CW in an outer area is denser than that in an inner area. A power supply terminal unit having connection wires for supplying electricity to the heating element CW is arranged in the center on the back side of a silica glass plate-like member 2. Connection wires 4a and 4b connected with the heating element CW in the inner area are connected with the heating element in the inner area in the center of the silica glass plate-like member. Connection wires 3a and 3b connected with the heating element in the outer area are extended from the center of the silica glass plate-like member toward the outer area and connected with the heating element CW in the outer area, without intersecting the heating element CW in the inner area.