PURPOSE: To attempt improvement of engine properties by forcing those pistons sliding in a cylinder by dividing the inside of a cylinder into two parts to face to each other and connecting them to corresponding crank shafts by means of respective connecting rods, so as to enable silent operation.

CONSTITUTION: A crank shaft 1 is provided on one part, while a crank shaft 2 is provided on the other part on the opposite side thereof. A cylinder 3 is arranged in the center part, and a piston 4 and a piston 5 are inserted therein. The piston 4 is connected to the crank shaft 1, and the piston 5 is connected to the crank shaft 2 by respective connecting rods. An intake port 6 and an exhaust port 7 are provided near the top of the pistons, and respective ports are operated by being interlocked with the corresponding crank shafts. And a sparkling plug or a fuel injection device 8 is provided near the top of the pistons, so as to assemble a complete set of engine. Both crank shafts 1, 2 are connected to each other by somewhat deviating their phases. Thus, the silent operation can be performed by newtralizing and offsetting vibration, and engine properties can be improved.