A desk top extension device which readily increases the work area of a desk without need for any modification to the desk is structured for being used in conjunction with a partially opened uppermost desk drawer and is composed, in essence, of a substantially rectangularly shaped base member and an interconnection system composed of an extension member and an abutment member connected thereto. In operation, the topmost desk drawer is partly pulled out and the extension member is inserted into the desk drawer on an angle then horizontally oriented so that the abutment member is located within the desk drawer abutably against the desk frame. Thusly, the base member rests upon the front top edge of the drawer and the abutment member holds the desk top extension device from tipping and moving outwardly from the desk. A book rest member may be connected with the base member for holding reading material in a comfortable orientation for reading thereof by the desk user.