COOLING STRUCTURE FOR ENGINE, ENGINE, AND VEHICLE

A cooling structure of an engine comprises a cylinder block provided with a wall surface partitioning a water jacket provided to surround a cylinder line and allow cooling water to flow therein and a water-jacket spacer arranged inside the water jacket and provided to regulate flowing of the cooling water. The water-jacket spacer comprises a spacer body having a shape along an outer-peripheral shape of the cylinder line and includes an internal surface facing cylinders, and an expansive member expandable according to an external factor is provided at the internal surface of the spacer body such that the expansive member extends continuously over a range from an one-end side to the other-end side of the cylinder line at a lower part, in a cylinder-axis direction, of the internal surface of the spacer body.