PURPOSE: To regulate elongation of a trough body and to prevent wear of the trough body and break of heat insulating material by fitting a trough fixing member for engaging with joint part connected to an outer frame with heat resistant mortar and a trough holding member for abutting on the upper face of the joint part inserting heat resistant packing in a cover part.

CONSTITUTION: Execution of work for the body part 9 forms the outer frame 6 and successively, after laying molten metal leakage sensor 13 at bottom face of the outer frame 6, the heat insulating material 7 is set in the outer frame 6 and successively, two blocks 8a, 8a are set in each divided frame 6a while inserting the heat resistant packing 11 to the joint part of intermediate part B. Then, each block 8a is connected to the block 8a set at the adjacent divided frame 6a in the joint part of outer end part A with the heat resistant mortar under condition of inserting each plate 12. Further, at center of longitudinal direction of each cover part 10, one pair of the trough holding members 16, 16 at right and left abutted on upper face of the joint part at B are closely fitted to the cover plate 10a, and floating-up at the joint part in the block 8a can be prevented. By this method, the elongation of the block is regulated in sticking-out direction from the divided frame.