While enlargement of cover members attached to an engine body is avoided, the flexibility of the shapes of the cover members is increased and it is made possible to lead to a predetermined position drainage discharged from a cooling water pump attached to the external surface of a lateral wall of the engine body. A drainage discharge hole for discharging drainage is provided in a lower portion of a pump case. An engine side rib leads downward drainage discharged from the drainage discharge hole is integrally provided on an engine body forming part of the engine body so as to project from an external surface of a lateral surface thereof.