To lower vibration and noise, by arranging inside cylinders on an outside piston, arranging in the inside cylinders, an engine upper part formed by airtightly fitting and inserting a pair of inside pistons and an engine lower part including an inner bottom piston in which an electromagnet is embedded, and supplying pressure oil generated to a hydraulic turbine.

When an engine is started, fuel and oxygen are sequentially ejected to insides of air cylinders 2 having a predetermined timing so as to be ignited, and outside pistons 11, inside pistons 12a, 12b and inner bottomed pistons 20 are vertically moved. At this time, the inside pistons 12a, 12b are connected to each other by oil pipes 15, and in the case that one air cylinder 2 is in an intake stroke and an explosion stroke, the other air cylinder 2 is moved so as to be in a compression stroke and an exhaust stroke. Piston rods 16 extended on the bottom end surfaces of the outside pistons 11 are connected to and integrated with the inner bottom pistons 20 through electromagnets 24 embedded in the inner bottom pistons 20. Then, pressure oil by the inner bottom pistons 20 is fed to a hydraulic turbine 41 so as to drive the hydraulic turbine 41, and power from a transmission shaft is taken out.