A power plant which is capable of enhancing the driving efficiency and the power-generating efficiency thereof. A rotating machine includes a first rotor having a magnetic pole row that has each two adjacent magnetic poles, a stator having an armature row that is disposed in a manner opposed to the magnetic pole row, for generating a rotating magnetic field between the armature row and the magnetic pole row by a predetermined plurality of armature magnetic poles, and a second rotor having a soft magnetic material element row that is formed by a plurality of soft magnetic material elements arranged in a manner spaced from each other. The ratio between the number of the armature magnetic poles, the number of the magnetic poles, and the number of the soft magnetic material elements is set to 1:m:(1+m)/2 (m≠1.0).