A power plant which is capable of reducing the size and costs thereof and attaining high driving efficiency. In the power plant 1, the ratio between the number of first armature magnetic poles that form a first rotating magnetic field generated by a first stator 23 of a first rotating machine 21, the number of first magnetic poles 24a of a first rotor 24, and the number of first soft magnetic material elements 25a of a second rotor 25 disposed between the two 23 and 24 is set to 1:m:(1+m)/2 (m≠1.0), and the ratio between the number of second armature magnetic poles that form a second rotating magnetic field generated by a second stator 33 of a second rotating machine 31, the number of second magnetic poles 34a of a third rotor 34, and the number of second soft magnetic material elements 35a of a fourth rotor 35 disposed between the two 33 and 34 is set to 1:n:(1+n)/2 (n≠1.0). The two stators 23 and 33 are connected to each other. The first and fourth rotors 24 and 35 are connected to driven parts DW and DW, and the second and third rotors 25 and 34 are connected to an output portion 3a of a heat engine 3.