To realize a double acting cylinder type explosion engine so as to provide a highly efficient engine.
In a double acting single cylinder explosion engine, an auxiliary member for optimizing the suction stroke is arranged so that the burning gas is not sucked by a piston and that the burning gas is sucked by the auxiliary member. An engine is formed of a cylinder 2 and a piston 3 to be slid therein, and a through shaft is fitted to the same shaft with a center shaft of the piston, and this through shaft is divided into two semi-shafts 4, 5 having the same dimension and the same shape by the piston, and these semi-shafts are respectively formed of auxiliary pistons 14, 15 to be slid inside of suction chambers 10, 11, and narrow diameter parts 12, 13, in which the suction gas passes through so as to achieve each explosion chamber through heads 8, 9, a hole part, and a leak or a clearance part, and an exhaust hole 21 is formed at a central part of the cylinder 2. The engine is connected to at least one connecting rod, and generates the explosion twice during one rotation of the connecting rod at 360 degree.