A cooling water passage structure for connecting cooling water passages in cylinders forming a V-shape in a water cooled type V-shaped internal combustion engine. A front cooling water passage of a front cylinder communicates with a front cooling water passage of a front cylinder head. A rear cooling water passage of a rear cylinder communicates with a rear cooling water passage of a rear cylinder head. Water pipes and cylindrical portions project from opposed positions of the front and rear cylinders and extend in one straight line. A connecting pipe is formed of rubber and is inserted in the water pipes. Ring clips and are engaged with annular grooves formed on the outer circumference of the connecting pipe at the front ends of the water pipes. O-rings are engaged with the outer circumference of the connecting pipe near the opposite ends thereof. The water pipes are connected to each other in a water tight manner.