To greatly increase the total efficiency of saving energy by actualizing highly efficient connection of a hydraulic motor while utilizing the conversion of explosion energy directly into hydraulic pressure.

A sliding shaft is fixed and mounted onto the upper part of one piston, and a through-hole is provided in a cylinder head. In the state of securing the air tightness of the reciprocating-motion sliding shaft fixed to the piston, explosive force that the piston receives through the through-hole of the cylinder head is used for reciprocating motion to take out energy to the outside of the cylinder. The sliding shaft is connected to the hydraulic piston to convert explosive pressure directly into hydraulic pressure. Without taking an output out of the crank shaft of an engine, the hydraulic pressure is converted into torque as motive power with the hydraulic motor. The energy is accumulated once so that the engine is constantly revolved with optimum efficiency for ON-OFF repetitive operation. The hydraulic motor is installed directly on a tire wheel to easily collect brake energy.