To aim at lowering of cost, thinning and energy saving of a heater by accurately controlling heating temperature by restraining heating from above a heated object in heating the heated object by radiation heat between heaters arrayed in parallel top to bottom.

A plurality of panel heaters 3 are provided arrayed in parallel with each other with an interval along a vertical direction. Each heater is provided with a heat-radiating body 10a, a top cover 10b covering a top face of the heat-radiating body 10a and a bottom cover 10c covering a bottom face of the heat-radiating body 10a. Heated objects 4 placed between the heaters 3 are heated with heat radiated from the top face side and that radiated from the bottom face side of each heater 3. Emissivity of the bottom cover 10c is set lower than that of the top cover 10b, so that heat radiant quantities from the bottom face side of each heater 3 per unit of time is suppressed than that from the top face side.