Cooling structure for internal combustion engine

A spacer (14) arranged inside a water jacket (13) which is formed to surround peripheries of cylinder bores (12a) in a cylinder block (11) of an internal combustion engine includes support legs (14e, 14f, 14g, 14h) extending in an up-and-down direction from a spacer main body part (14a) which partitions the water jacket (13) into an upper and lower cooling water passages. The support legs (14e, 14f, 14g, 14h) are disposed in opposite end portions in a cylinder row line (L1) direction, where the temperatures of the cylinder bores (L1) tend to be lower. Accordingly, even if the flow of cooling water is more or less inhibited by the support legs (14e, 14f, 14g, 14h) and the cooling effect deteriorates, it is possible to prevent the temperatures of the respective cylinder bores (12a) from becoming different by suppressing the influence to a minimum.