PURPOSE: To make it difficult to see the trace of screwing even in changing the height for providing a nice look by forming two front and rear rows of a plurality of recesses vertically extending on the inner surfaces of both side plates and screwing supports in the recesses respectively for mounting a rack thereon.

CONSTITUTION: Two front and rear rows of a plurality of recesses 4 vertically extending are provided on one inner sides of partition plates 2 respectively, and knurled rack supports 1 are screwed in the recesses so that a rack 3 is mounted on the supports 1. When the height of the rack 3 is changed, the remaining flaws are difficult to see even if the screwed portion of the rack support 1 is straight screwed, since the depth of the recess 4 is large enough. Also, since the support is screwed in, it is not easily removed so that the height of the rack 3 can be adjusted variously.