Abstract: A high-pressure multistage pump is used for supplying liquid to facilities such as boilers under a high discharge pressure. The high-pressure multistage pump has a barrel-shaped outer casing, an inner casing housed in the barrel-shaped outer casing, a cover sealingly closing an axial end of the outer casing, a pump shaft rotatably supported in the inner casing and the cover, and an array of impellers mounted on the pump shaft. One of the impellers has a suction chamber positioned most closely to the cover and held in communication with an inner space which is jointly defined by the outer casing, the inner casing and the cover.