PURPOSE: To improve reliability for data by controlling a magnetic disk device with a current driving system since the problem of a noise or a torque ripple exists in the R/W state of the magnetic disk device, and employing a voltage driving system in a non-R/W state to reduce heat generation.

CONSTITUTION: In the current driving system, a reference pulse signal 2 is phase-compared with a Hall element output signal 6 at a phase comparator 3, and an error is detected from a motor 27 setting circuit, and pulse width is modulated corresponding to the error, then, a pulse width modulation signal 7 can be obtained. After that, the signal 7 is smoothed by inputting to a low- pass filter 8, and analog linear control signals 9 are outputted from linearly operated transistors Q2, Q4, and Q6, and those signals are inputted to a transistor control circuit 14. Next, in the voltage driving system, since it is enough to reduce the heat generation in a transistor at an output stage, the revolution of a motor 27 is controlled, and in the current driving system, a constant voltage can be varied by using a switching regulator 13 in this stage.