A structure of a water pump is provided without increasing the cost
thereof, or without enlarging the size to improve the durability of the
water pump. A seal apparatus having a seal ring 13 and a slinger 14 in
combination to prevent foreign matter from progressing into the rolling
bearing 6a. The amount of compression .delta. of the second seal lip 23,
which occurs when the tip edge of the second seal lip 23 of the seal ring
13 comes in contact with the outer peripheral surface of the
outer-diameter-side cylindrical section 26 that is formed at the outer
peripheral edge of the slinger 14, is at least 1/10 and up to 7/10 the
height of the second seal lip 23 in the free state. In addition, the
roughness of a portion of the outer peripheral surface of the
outer-diameter-side cylindrical section 26 which the tip edge of the
second seal lip 23 comes in sliding contact with is from 0.2 .mu.m to 2.0
.mu.m in the arithmetic mean Ra, or is from 0.8 .mu.m to 8.0 .mu.m in the
maximum height Ry.
