PURPOSE: To maintain self-priming capability, and to enable restarting to be carried out in a short time by providing a reserve tank separately from the main pipe, and forming to the main pipe an inflow port and an outflow port, which are communicated with the reserve tank, so as to have a space in the vertical direction.

CONSTITUTION: A self-priming liquid supply device 4 is provided in the line of the suction-side main pipe 3 ranging from a pump chamber 1 to the suction port 2. A discharge-side main pipe 5 ranges from the pump chamber 1 to a discharge port 6. In the self-priming liquid supply device 4, an annular reserve tank 7 is integrally provided around the suction-side main pipe 3. In the suction- side main pipe 3, an inflow port 8 and an outflow port 9 which are communicated with the reserve tank 7 are formed. When a siphonic effect is produced, the liquid inside the reserve tank 7 flows out by gravity into the suction-side main pipe 3 through the outflow port 9, and flows into the pump chamber 1 to become self-priming liquid. Thus, self-priming capability can be maintained, and restarting can be enabled to be carried out in a short time.