To provide a desk mat for a study desk with a shelf by which positioning is easily performed in installing onto a top board without falling backward and the upper surface of the top board is effectively utilized, concerning the desk mat to be used for the study desk with an on-desk shelf placed in the rear part of the top board.

The desk mat 1 is used for the study desk 2 with the shelf where the on-desk shelf 4 having at least both side boards 5 is placed in the rear part of the top board 3. Notched parts 12 for receiving both the side boards of the on-desk shelf are formed in both the rear parts of a sheet. A horizontal width is made to substantially coincide with the effective horizontal width of the top board. Step parts 13 to be abutted onto the front end of each side board of the on-desk shelf are arranged in the both side rear parts so as to form the notched parts 12.