A main bearing for a crankshaft of an internal combustion engine comprises a pair of semi-cylindrical bearings. An oil groove extends on an inner circumferential surface of one semi-cylindrical bearing in a circumferential direction so that the center thereof in an axial direction aligns with that of an inlet opening of a lubricating oil path in a journal section of the crankshaft. The oil groove does not extend up to an axial direction groove formed at a joint portion of the semi-cylindrical bearings so that a separation inner circumferential surface extends between a circumferential direction end portion of the oil groove and the axial direction groove. The length of the separation inner circumferential surface is smaller than that of the inlet opening in the circumferential direction.