To provide a cooling water pipe of an engine allowing easy installation and removal of an oil filter and preventing the attachment of the oil to a hose for cooling.

A groove 18 is formed to a cover main body 14, a cutting 19 is formed to an outer peripheral wall 15 to communicate to the groove 18, the cover main body 14 is opposed to an oil filter 4, the cutting 19 is faced between hose parallel parts 12a and 12b, and a hose cover 13 is installed to hoses 8 for cooling. Even though the oil drops down temporarily in the oil filter 4 installing and removing time, the oil is received by the cover main body 14, and discharged between the parallel parts 12a and 12b from the cutting 19 passing through the groove 18. As a result, the oil does not drop to the hose 8 for cooling water, and the attachment of the oil can be prevented. Since it is not necessary to take out the engine cooling water, and to remove relay hoses 7a and 7b, in the installing and the removing time of the oil filter 4, the working process number and the working time can be reduced, and the installing and the removing work of the oil filter 4 can easily be carried out.