A magnetic bearing device includes a main shaft (13), a flange shaped thrust plate (13a) coaxially mounted on the main shaft so as to extend perpendicular to the main shaft and made of a ferromagnetic material, a rolling bearing unit for supporting a radial load and a magnetic bearing unit for supporting one or both of an axial load and a bearing preload, an electromagnet (17) fitted to a spindle housing (14) so as to confront the thrust plate, without contact, a sensor (18) for detecting an axial force acting on the main shaft, and a controller (19) for controlling the electromagnet in response to an output from the sensor. In this magnetic bearing device, the stiffness of a composite spring formed by the rolling bearing unit and a support system for the rolling bearing unit is so chosen as to be higher than the negative stiffness of the electromagnet.