In order to obtain an electromagnetic rotating machine of lightweight and
high energy efficiency, which produces big torque for rotating a
large-diameter fan, a coil A and coil B as excitation coils are disposed
on an inner peripheral surface of a fan casing so as to face an outer
circumference of the fan, and a coil M as an armature coil crosses at a
central portion and is disposed on the outer circumference of the fan.
The relationships |I.sub.ai|=|I.sub.ai+1| and I.sub.ai=-I.sub.ai+1, or
|I.sub.bi|=|I.sub.bi+1| and I.sub.bi=-I.sub.bi+1 are obtained
respectively for the coil A or coil B by a current control device (not
shown). Moreover, the coil A and coil B are subjected to excitation
control such that the direction of effective electromagnetic force, which
is generated by an interaction between an effective magnetic field formed
by the coil A and effective induced current applied to the coil M by the
coil B, corresponds to the direction of rotation of the fan.