An eccentric disc grinder (1) has a housing (3) in which a motor (11) rotates a grinding disc (45) by means of a driven shaft (31) on a circular path and at the same time around its axis (49). The driven shaft (31) is rigidly coupled in rotation to an eccentric carrier (35) that carries an eccentric pin (37) rigidly coupled in rotation to the griding disc (45) and rotatively mounted, in particular in a rolling bearing (39), with a determined bearing friction and with a determined eccentricity 'e' with respect to the driven shaft (31). The grinding disc (45) moves in circles around the axis (32) of the driven shaft (31) with eccentricity 'e' and at the same time, because of the bearing friction, rotates around its own axis (49) or that of the eccentric pin (37). In order to prevent the grinding disc (45) from accelerating up to the speed of rotation of the driven shaft, the speed of rotation of the grinding disc (45) is modified depending on the perpendicular force that acts on its working surface (47), in that a motor speed regulator automatically sets a higher speed of rotation when the perpendicular force is increased and a lower speed of rotation when the perpendicular force is reduced.