To reduce pulsation of discharge pressure by providing a pulsation/ noise reducing extended chamber to either a suction passage extended from the suction port of a pump caging assembly to a pump chamber or a discharge passage extended from the pump chamber to the discharge port.

A suction passage 49 through which a suction port 7 and a pump chamber 13 are communicated with and connected to each other, and a discharge passage 51 through which a discharge port 9 and the pump chamber 13 are communicated with and connected to each other, are formed as internal passages in a casing main body 1. Pulsation/noise reducing extended chambers 53, 55 are respectively arranged on the way the suction passage 49 and the discharge passage 51, that is, on the way of internal channels between the suction port 7 and the pump chamber 13 and the pump chamber 13 and the discharge port 9. The extended chambers 53, 55 are equipped with end members 61, 63 for varying the capacities of the extended chambers 53, 55 and extended chamber capacity adjusting screws 65, 67 for regulating a position in a depth direction. Hereby, the extended chambers 53, 55 reduce pulsation in a specific frequency range in a pump casing assembly 1 by mutual interference action between incident pressure wave and reflective pressure wave.