The occurrence of fluctuations in liquid chemical during the discharge and intake thereof in a device that employs a liquid chemical supply pump 10 that discharges liquid chemical taken in by means of a change in volume inside a pump chamber 16 that accompanies the displacement of a bellows type partition 14. The amount of fluctuation in the bellows type partition member 14 that accompanies the operation of a discharge side valve 32 will be detected by a displacement sensor 58. The amount of fluctuation is a parameter that indicates a correlation with the abrupt flow of liquid chemical that accompanies the opening of the discharge side valve 32. Thus, the amount of fluctuation will be reduced, and the pressure inside a pump chamber 16 prior to the opening of the discharge side valve 32 will be controlled.