To provide a fuel injection valve installing structure to an internal combustion engine having high cooling efficiency by using a cooling medium of circulating in the internal combustion engine and a radiator.

A fuel injection valve installing hole 19 and a cooling medium flow passage 21 conventionally separately arranged by an engine head 20 communicate with each other. A communicating passage 16 is formed of one or more places to respective fuel injection valves, and the cooling medium flow passage 21, the communicating passage 16 or the fuel injection valve installing hole 19 are arranged so as to have flow speeds when a cooling medium contacts with the fuel injection valves. For preventing the cooling medium from flowing out to the outside of a flow passage by arranging the communicating passage 16, a clearance between the engine head 20 and the fuel injection valves seals fuel by installing seal parts of one or more places in a fuel injection valve upper part and a lower part.