Abstract: A panel heater with a flat metal sheet of substantially even thickness of from 0.06 to 0.2 mm and having a mesh-like radiation section formed in the central portion of the sheet, the mesh-like radiation section being composed of a plurality of units of wave-like current passageways of uniform width of approximately 2 mm from one end to the other, arranged parallel to each other and connected to each other at the crests of the wave-like current passageways so that the combined width of the passageways at the crests is twice the uniform width. The panel heater also has a pair of heat resistant boards between which the metal sheet is sandwiched; and a frame assembly joining together the heat resistant boards.