[en] Thermal loads received at the surface of a divertor plate distribute intensely in the poroidal direction and have a peak as shown by a gauss distribution. Then, a nuclear exothermic material is disposed on the side opposite to plasmas for increasing nuclear heat, and the shape of the nuclear exothermic material is determined corresponding to the thermal load received at the surface on the side of plasmas so as to equalize the thermal expansion between the side of plasmas and the side opposite thereto. Then, the thermal expansion is balanced between both sides of the divertor plate to prevent a great bending deformation. Further, since the bending deformation is reduced, the reliability of the sliding portion in a case of using a sliding support for the divertor plate is increased, thereby enabling to keep the position of the surface accurately. (N.H.)