To prevent a cooling water pooled on the bottom of a drain pocket from leaking outside through a minute gap due to capillarity to eliminate the risk of being misidentified to be occurrence of water leakage.

A water pump is provided with a drain pocket 15 for pooling the cooling water leaked out of a seal part. The drain pocket 15 is composed of a horizontal hole 13 opened to a pump body 2, and a plug 31 fitted to the opening of the horizontal hole 13. The plug 31 includes an overflow hole 34 for discharging the cooling water pooled in the drain pocket 15 to the outside, and a protrusion 33 covering at least an upper portion of the overflow hole 34.