A power plant 1 for driving driven parts DW and DW includes a prime mover 3, and first and second generator-motors 20, 30. The first generator-motor 20 is comprised of a first stator 22, a first rotor 21 formed by magnets, and a second rotor 23 formed by soft magnetic material elements and disposed between the first stator 22 and the first rotor 21. The second generator-motor 30 is comprised of a second stator 32, a third rotor 31 formed by magnets, and a fourth rotor 33 formed by soft magnetic material elements and disposed between the second stator 32 and the third rotor 31. The first and fourth rotors 21, 33 are mechanically connected to the driven parts DW and DW, and the second and third rotors 23, 31 are mechanically connected to an output shaft 3a of the prime mover 3.