PURPOSE: To install a washing machine placing pan having the incorrect dimension without using an auxiliary board in the conventional.

CONSTITUTION: A recessed part 23 having the depth for the accommodation of a weir part 25 at the front part of a washing machine placing pan 24 is formed downward or a thin part for forming the recessed part is formed at the outer lower front part of an outer shell constitution member 11 (rear side part of the front leg part 21 of a base plate 13). The recessed part 23 is formed as it is or in cutting form from the thin part, by providing a closing plate which closes the formation of the recessed part and can be mounted and demounted, or the closing plate is demounted, an the weir part 25 at the front part of the washing machine placing pan 24 is enclosed, and a washing machine can be placed on the washing machine placing pan 24 without getting over the weir part 25.