Bearing case for engine

A main bearing case(7) has a bearing holder(61) for holding a bearing(11a) so as to support a crankshaft(12), and a crankcase mounting section(62) at which it is joined to a crankcase(3). Rib walls(63) are provided so as to surround the bearing holder between the bearing holder and the crankcase mounting section. The rib walls are formed in a side of the crankcase, and in a neighborhood of each inner side face of the bearing holder and the crankcase mounting section. These rib walls receive a force exerted in a radial direction from the crankshaft. Thereby, an improvement of rigidity of the main bearing case can be achieved, and also the lubrication to a valve-operating system(30) can be always ensured by preventing an oil surface from lowering even when an engine is located with inclination.