PURPOSE: To realize a high magnetic field and the uniformity of the magnetic field by forming a ring-shaped projecting section concentric with a coil device to the inward section of a magnetic substance surrounding the coil device.

CONSTITUTION: Ring-shaped projections 9a, 9b concentric with a coil davice are shaped to the inward section of a core 1 as a magnetic substance surrounding main magnetic-field generating coils 3a, 3b and inclined magnetic-field generating coils 4a, 4b as the coil device. The sectional shapes of the projections 9a, 9b take a simple shape such as a rectangle, a circle, an ellipse, etc., and the number of the projections formed is brought to at least one or more. Accordingly, not only the effect of the uniformity of a magnetic field with the formation of a salient pole is acquired but also the projections 9a, 9b are shaped in structures smaller than conventional salient poles, thus miniaturizing and lightening the core 1 as the magnetic substance, then realizing equality in the same manner as the salient pole.