PURPOSE: To enable to prevent vibration of a reciprocating internal combustion engine, by minimizing shifting of the center of gravity of the engine by disposing cylinders in an opposed manner so that the driving force is acted symmetrically to a crankshaft.

CONSTITUTION: Cylinders 2, 3 of the same size are disposed symmetrically with respect to the axis of a crankshaft 1. One piston 4 is connected to the crankshaft 1 via a bifurcated connecting rod 6 while another piston 5 is connected to the crankshaft 1 via a connecting rod 7 to located between the bifurcated portions of the connecting rod 6. Here, each of the suction, compression, explosion and exhaust strokes of the two cylinders 2, 3 is controlled to synchronize with each other, so that the driving force of the connecting rods 6, 7 is acted symmetrically to the crankshaft 1. Since, with such an arrangement, almost no shifting of the center of gravity of the engine is caused, it is enabled to prevent generation of vibration.