<p>A chemical liquid supply pump enabling a diaphragm to be securely deformed to an operating chamber side in a short time and capable of reducing a time for filling a chemical liquid into a pump chamber and sufficiently securing the filling amount of the chemical liquid. The opening (22d) of a supply/discharge passage (22b) is positioned at the center part of the inner wall surface (22c) of the operating chamber (26) (recessed part (22a)), and a cross-like vent groove (22e) extending from the opening (22d) of the supply/discharge passage (22b) to the peripheral edge part of the inner wall surface (22c) is formed in the inner wall surface (22c) of the operating chamber (26). Since an operating air in the operating chamber (26) is discharged (sucked) through the supply/discharge passage (22b) in sucking the chemical liquid, a pressure in the operating chamber (26) becomes negative. Since the opening (22d) communicates with the vent groove (22e) extending to the peripheral edge part of the operating chamber (26), if such an event that the center part of the diaphragm (23) first covers the opening (22d) portion of the supply/discharge passage (22b) occurs, the operating air in the operating chamber (26) can be continuously discharged (sucked) from the vent groove (22e) positioned on the outside of the center part which first comes into contact with the opening (22d) of the supply/discharge passage (22b).</p>
