A crankshaft of an internal combustion engine has journals provided with shaft oil passages for carrying the oil to crankpins, and guide grooves having parts in which the shaft oil passages open, respectively, and opening in the cylindrical surfaces of the journals, respectively. The guide grooves has downstream end parts into which the shaft oil passages open, respectively, and extend in a circumferential direction in which the crankshaft rotates from the downstream end parts, respectively. First half bearing members of bearings are provided in their bearing surfaces with oil grooves through which the oil is supplied to the guide grooves, respectively. Each of the oil grooves are diametrically opposite to each of the guide grooves. The oil grooves have an axial width (W5) smaller than the axial width (W3) of the guide grooves. Thus oil leakage from gaps between each of the bearings and each of the journals of the crankshaft is reduced and hence an oil pump having a small capacity can be used.