In a sanding machine, a wood panel (2) is fed underneath a sanding device (10) having an abrasive belt (11) which is wound in a ring shape around a tensioning drum (13) and a drive drum (12) defined by a cylindrical sleeve (21) fitted in a rotatory way on a support shaft (16), which is moved from a lowered operating position to a lifted rest position by an actuating device (24) connected to the support shaft (16) through the interposition of a pneumatic shock absorber device (28); the supply pressure of the pneumatic shock absorber device (28) being selectively controlled as a function of a width of the panel (2).