PURPOSE: To obtain a structure in which the cleaning of a drain port is facilitated by allowing the part above the port operable without removing a bottom plate by transferring an article on the plate to the other to clean the port.

CONSTITUTION: A bottom plate extended from the lower end to rear water is provided at a return grill 32 having a cold air circulating passage 5 between an outer box 5 and an inner box 3 and a suction port 5b at the rising upper end of the lower front surface of the box 2 for forming an interior 4 inward. The plate 31 is reduced at the front end of the plate as compared with that of prior art. At the time of cleaning a drain port 21 provided at the lowermost part of the box 2, a small quantity of articles placed on the plate are transferred to an adjacent bottom plate 31, and the grill 32 is removed to open above the port 21, and can be cleaned. Thus, the transfer of a large quantity of articles on the plate 31 is eliminated, and the cleaning of the port 21 is extremely facilitated.