PURPOSE: To minimize the swing of a rotating body by providing a speed detecting means which detects the speed of a rotating body and a change-over means which changes over automatically an element determining the lock range of PLL(Phase Looked Loop) circuit so that it may be a constant corresponding to speed.

CONSTITUTION: The high attenuation generating circuit 15 (PLL circuit) of a controller 10 detects the amplitude and phase of the swing component synchronous with the speed of a rotating body according to the output signal S1x of a x-axis position sensor 11x and a rotational synchronizing signal S2 and outputs the second x-axis control signal S4x and y-axis control signal S4y with more leading phase than the swing component at the frequency corresponding to the speed of the rotating body. The circuit 15, provided with a constant change-over circuit, makes change-over so that the element such as condenser which determines the lock range of the above PLL circuit may be a constant corresponding to the speed of the rotating body. As a result, the lock range is changed over automatically according to speed, and the speed is increased or decreased with phase leading signal ON.