PURPOSE: To attach a reinforcing member easily by a method wherein a positioning hole for the reinforcing member is formed on the front surface of a partitioning part, and an engaging piece which engages with the positioning hole is provided on the reinforcing member.

CONSTITUTION: When central doors 28, 29 are attached to an internal box 23, a reinforcing member 47 is inserted from the rear side of a partitioning part 27 and moved to the front side, and engaging pieces 49a, 49b are put in positioning holes 48. Then, the reinforcing member 47 is brought into contact with the rear side of the partitioning part 27, and the engaging pieces 49a, 49b are engaged with the positioning holes 48. By doing this, the reinforcing member 47 is engaged at a fixing position. Thus, the work can be performed while confirming the reinforcing member 47, and therefore, the attaching work at a narrow space of the partitioned section becomes easier, and the reinforcing member can be accurately attached. For this reason, the working period of time in the manufacturing process can be reduced.