PURPOSE: To widen application range by switching the polarity of one of (N+1)/2 exciting phases thereby switching the exciting pattern sequentially and repeating pre-excitation pattern and post-excitation pattern at an intermediate stage.

CONSTITUTION: Among exciting phases A-E constituting a radial connection through switching means (Tr1, Tr2)-(Tr9, Tr10), (N+1)/2 and (N-1)/2 phases are connected, respectively, with positive and negative phases in order to perform N-phase excitation. At that time, the switching means (Tr1, Tr2)-(Tr9, Tr10) switch the polarity of one of (N+1)/2 exciting phases and repeats pre- excitation pattern and post-excitation pattern at an intermediate stage. According to the invention, application range can be widened.