A main bearing for a crankshaft of an internal combustion engine has first and second half bearings forming an axial groove on an inner circumferential surface of a butting portion. Each half bearing has a main cylinder portion including a central portion, and crush relief portions each extending toward the central portion from an end surface of the half bearing with a center angle of 3° to 15°. A plurality of crush relief grooves are formed in each crush relief portion in the circumferential direction to communicate with the axial groove. An oil groove is formed in the circumferential direction on an inner circumferential surface of the first half bearing. The second half bearing has a transition region having an inward protruding curved surface a wall thickness of which becomes thinner toward the crush relief portion from the main cylinder portion.