PURPOSE: To enable to reduce diameter of a pump and to decrease pulsation on the exhaust side by arranging an intake valve and an exhaust valve vertically side by side and forming circular chamber above an exhast chamber.

CONSTITUTION: A separator 5 has a projected portion 6 at its center and a circular exhaust valve 7 is arranged on the external circumference of the projected portion 6. An in-chamber 14 which divides the space above the separator 5 into an upper intake chamber 12 and a lower exhaust chamber 13 is inscribed to an out-chamber 3 to be press-fitted therein. An intake valve 16 is fixed to the top side of a projected portion 15 of the in-chamber 14. And a circular chamber 19 is formed on the opper side of said chamber, and the external circumference of this chamber is press fitted into an out-chamber 3. Air gathers inside this circular chamber 19 and this air becomes damper of the pulsation pressure, thereby pulsation is lowered.