To solve the problem in the reciprocating of a power piston in sliding contact with the inner wall of a cylinder, which results in a large mechanical drive loss, or poor efficiency in a low temperature difference.

Each of displacer body parts 10 and 10 comprising semilunar rotors 11b and 11b housed in a pair of housings 14 and 14 so as to be mutually reversely rotatable by shafts 12 and 12 alternately generates a pressurized state and a negative load state to drive a vibrating plate 33c in a voice coil generator 30 from both sides, and the reverse drive is performed so as to be matched to the resonance frequency of the vibrating plate 33c. Therefore, power generation can be performed while minimizing the mechanical drive loss of the vibrating plate 33c. Since a displacer drive motor 20 is driven by an output of the generated power, the mechanical link in the drive of a rotary displacer 11 is interrupted. The displacer driver motor 20 with a small mechanical drive loss is used, whereby the mechanical drive loss is further reduced.