The invention intends to maintain a constant ink discharge amount among the recording heads, even in case a total pulse width of pulse voltages applied to heat generating resistors. For this purpose, a rank table is prepared in such a manner, even in a situation where a total pulse width of the pulses applied to the heat generating resistor is 3 μs or less whereby the ink discharge amount decreases with a decrease in the total pulse width, that a maximum reached temperature on the surface of the heat generating resistors at the application of a preheat pulse becomes higher with a decrease in the resistance of a rank resistor, and a pulse width P1 on the rank table is made longer thereby compensating a decrease in the ink discharge amount with a decrease in the total pulse width and maintaining a constant ink discharge amount.