Auxiliary machinery mounting structure of an engine

An auxiliary machinery mounting structure of an engine is provided, which can reduce the entire length of the engine, enhance the rigidity of a cover seal surface to improve the sealing effect, and also enhance the mounting rigidity of an auxiliary machinery. The auxiliary machinery mounting structure includes a mount seat (3a) that is integrally formed on an end surface of a cylinder block (3) extending vertically to a crank shaft of the engine to lie outward of and along a cover seal surface (3d) that is a surface engaging with a cover 10 laid over the end surface (3), and the auxiliary machinery (26) is mounted on the mount seat (3a).