PURPOSE: To enable control of a delivery amount of a pump with high precision, by a method wherein, based on a delivery pressure increasing velocity during rise of a delivery stroke, a pressure loss is calculated, and based on the pressure loss, a delivery amount of the pump is controlled.

CONSTITUTION: A delivery pressure during rise of the delivery stroke of an ink pump 1 is inputted to a control circuit 12 by means of a sensor 11. In a control circuit 12, from the increase velocity of a current delivery pressure, a pressure loss is calculated, and the based on the calculated pressure loss, a pressure value, by means of which a delivery amount per a unit time is specified, is calculated. When the calculated pressure value is within a normal value, a driven stepping motor 10 of the ink pump 1 is controlled so that the pressure value is maintained. This enables prevention of a change of a delivery amount of a pump due to a change in viscosity of ink.