To surely restrain a shaft torsion resonance phenomenon, when the state of a system changes.

A shaft torsion vibration component detecting means 31 extracts only the shaft torsion vibration component from inputted electric amount, containing shaft torsion vibration component which is obtained from an AC-DC converter 3 or the periphery of an AC bus. A shaft torsion resonance vibration restraining control means 32 forms n-number of suppression signals for restraining SSR vibration from the shaft tortion vibration component. A signal switching means 33 selects a suppression signal, capable of surely and effectively restraining SSR in the present state of system, from among n-number output signals of the control means 32, according to the state of system such as a bus voltage and a transmission line current. The selected suppression signal is sent to an adder 8.