To improve wear resistance through securing to the maximum an area of a sliding surface where bearing holes of connecting rods and a crank pin contact with one another when two connecting rods are supported by a common crank pin.

First chamfered portions 30, formed between first thrust supporting surfaces 32 that are provided on positions opposed to crank arms 28 of the two connecting rods 19 supported by the crank pin 26 and the bearing holes 23, are made larger than second chamfered portions 31 formed between second thrust supporting surfaces 33 that are respectively provided on positions where the two connecting rods 19 are opposed to each other and the bearing holes 23. Thereby, widths W of bearing metals 24 are secured to the maximum avoiding interference between the connecting rods 19 and filet portions 29 of the crank shaft 11, so that the wear resistance of the bearing metals 24 can be improved.