A target PES value input from a controller and a value from a PES value calculator which corresponds to the displacement of a magnetic head are synthesized. A coefficient applicator applies a predetermined coefficient K.sub.1 to the above deviation (multiplication), and a variable coefficient applicator applies a coefficient K.sub.a to the resulting value. The coefficient K.sub.a is varied and set in the variable coefficient applicator in accordance with a value input from a table. The correspondence between the target PES value and the coefficient K.sub.a used as a feedback coefficient for the PES value is stored in the table in advance so that the coefficient K.sub.a is small when the PES value varies sharply and so that the coefficient K.sub.a is large when the PES value is small. The variable coefficient applicator outputs, to a driver, a value to which the coefficient K.sub.a has been applied in accordance with the value from the table.