Abstract: A planar heat generator comprises a heating element of metallic foil; a first pair of sheets made of a plastic material which are bonded to each other so that the heating element is interposed therebetween; a second pair of sheets made of a plastic material which are bonded to the outer surfaces of the first pair of sheets, respectively; and a pair of protective covers which are made of a plastic material having a melting point at least approximate to that of the material of the second pair of sheets. The protective covers are larger in area than the second pair of sheets and are bonded by fusion not only to the outer surfaces of the second pair of sheets, respectively, but also to each other at peripheral areas which extend beyond the peripheral margins of the second pair of sheets.