PURPOSE: To switch the polarity of an electromagnet without switching the polarity of a power source.

CONSTITUTION: A central processing unit 30 outputs a first power source current set value signal to a first power source control unit 34 on the basis of a control command to supply a current from a first power source 21 to an electromagnet 20. The central processing unit 30 outputs a second power source current set value signal to a second power source control unit 36 on the basis of the control command to supply the current from a second power source 22 to an electromagnet 20. The first power source 21 exclusive for (+) and the second power source 22 exclusive for (-) are provided, and respective output coils 24, 25 are wound on the iron core 23 of the electromagnet 20 independently, whereby the polarity of the electromagnet 20 can be switched without switching the polarity of the power source as in the past.