The present invention relates to a computer case for a desk having a variable width, which efficiently uses the space of a desk as a computer is installed under the desk and receives the computer therein regardless of the thickness of the computer by varying the width of the case. The computer case for a desk having a variable width, according to an embodiment of the present invention, comprises: left and right fixing brackets which are installed in the bottom of the desk in the same direction and has multiple fastenings in a longitudinal direction; a first case member which is installed in the longitudinal direction of the left fixing bracket and has multiple fastening holes where the fastenings are inserted; a second case member which has multiple fastening holes where the fastenings are inserted; and a fixing pin member which fixes the first case to the second case.
