PURPOSE: To eliminate the possibility of a failure in metallurgical joint surfaces by metallurgically joining a first wall to a supporting base plate only in the narrow areas in the central parts of armor tiles.

CONSTITUTION: Cooling pipes 9 and the armor tiles 4 are joined by metallurgical joining, such as brazing in vacant regions. Since the heat of the armor tiles 4 is efficiently cooled, the temp. of the armor tiles 4 is maintained sufficiently low. On the other hand, the joining regions to the supporting base plate 5 having high rigidity are the narrow regions 8 and, therefore, the thermal stress by a difference in the coefft. of thermal expansion is small and the problem of the crack in the metallurgically joined parts does not arise.