PURPOSE: To keep the ink discharge quantity constant regardless of a temperature change by setting ink discharge pressure balancing with a desired ink flow rate on the basis of an observed value.

CONSTITUTION: A solenoid valve is closed in a process S1, a pump is pressed up to first specified pressure in a process S2, the pump is fixed-pressure controlled at the first specified pressure and a flow rate at that time is measured as a first flow rate in a process S3, the pump is pressed up to second specified pressure in a process S4, the pump is fixed-pressure controlled at the second specified pressure and a flow rate at that time is measured as a second flow rate in a process S5, pressure balancing with a predetermined pressure is calculated by using the first specified pressure and the second specified pressure and the first flow rate and the second flow rate in a process S6, the pump is pressed up to balanced pressure in a process S7, and the pump is fixed- pressure controlled at balanced pressure in a process S8.