To minimize a cover body of an internal combustion engine, and to control the oscillation of a wall in the axial direction while forming a breather passage capable of smoothly introducing blow-by gas in an internal space, in the cover body covering the end of the engine body of an internal combustion engine from the axial direction and having a wall forming an internal space in conjunction with the end.

A wall 50 of a chain cover 40 forming a chain chamber 25 has a lower wall 53a facing the end of the engine body in the axial direction of a crankshaft 6, and a higher wall 53b facing the end of the engine body and more apart from the end than the lower wall 53a, and formed so as to be in a different level from the lower wall 53a through a different level part 51 in a first bank 40a. The higher wall 53b covers the end from the lower part of the cylinder block to the cylinder head, and forms a breather passage 54 for introducing blow-by gas in the crank chamber to an operation valve chamber.