PURPOSE: To enable the generation of noise to be decreased while the axial direction length of a crankshaft to be reduced with a less number of journal shafts, by providing one ends of the second crankpin shafts of be arranged in both ends of the first crankpin shafts respectively through the first arms.

CONSTITUTION: The first crankpin shafts B1', B3' provide in their both ends one ends of the second crankpin shafts B2', B4', placed in an angular position different from that of the crankpin shafts B1', B3', to be arranged respectively through arms C1', C3', and journal shafts A1'WA3' are provided to be respectively arranged in the other ends of these two crankpin shafts B2', B4'. In this way, a crankshaft is symmetrically formed with the crankpin shafts B1', B3' serving as the center. Further an engine connects the crankpin shafts B1', B3' with pistons E1', E3' by connecting rods D1', D3' and the two crankpin shafts B2', B4' with pistons E2', E4' by fork-shaped connecting rods D2', D4, consequently the engine, in which driving force of the pistons E1'WE4' acts on the crankshaft being prevented from deflecting to the axial direction, small decreases the generation of noise. While a number of the journal shafts A1'WA3' can be reduced.