PURPOSE: To prevent the immersion of a fine foreign substance between a key and a key groove to joint an impeller on a pump drive shaft and to prevent abrasion and gall of the aforementioned key and key groove.

CONSTITUTION: In a rotary liquid pump with a tubular core material 32 made of a material higher in rigidity than an elastic material buried on a boss part 31 of an impeller 28 made of the elastic material and with a pump drive shaft and the tubular core material 32 rotationally integrally jointed with each other by a key by way of inserting the pump drive shaft into the tubular core material 32, seal parts 45, 46 positioned at both side parts of a key groove 35 provided on the circumferential surface of the tubular core material 32 and extending in the axial direction are formed integrally with the boss part 31 by the elastic material.