There are provided a row of external permanent magnets and a row of internal permanent magnets; a floating output ring is provided on which is wound a 3-phase coil, between these rows. The floating output ring has no mechanical restraining relationship with any other member in the linear motor). Instead, a controller that controls a PWM inverter that injects AC exciting current into the 3-phase coil brings the central axes of the double cylinder and the floating output ring into coincidence by generating supporting force with respect to the floating output ring by magnetism, by controlling the d axis current component of the exciting current.