A bias magnetic flux is formed so as to be passed through the electromagnet core of an electromagnet, and a bypass magnetic path, serving as a magnetic path for a control magnetic flux, is formed in parallel with a permanent magnet, the bypass magnetic path being magnetized in a direction in which passage of the bias magnetic flux is blocked, and thus, even if the permanent magnet and the electromagnet are disposed in locations where the mutual magnetic fluxes of the permanent magnet and the electromagnet are superimposed, the control magnetic flux formed by the electromagnet is passed through the bypass magnetic path, whereby loss of the control magnetic flux can be suppressed. Thereby, the permanent magnet and the electromagnet can be disposed in locations where the mutual magnetic fluxes are superimposed, whereby the device can be made smaller in size.