To more accurately monitor the residual quantity of ink in a printer.

A CPU 31 receives print data from an external computer 38 through an interface 35 and reads out data concerning the residual quantity of ink from the recording element 42 in the ink cartridge 22 of a printer 11. The CPU 31 determines whether the ink ejection pattern is a continuous ejection pattern or an intermittent ejection pattern (1-5 levels) for each dot of each color from the print data, and then counts the number of dots of each ink ejection pattern. Subsequently, the CPU 31 reads out a predicted ejection ink weight from a ROM 32 and calculates the quantity of used ink from the number of dots of each ink ejection pattern and the predicted ejection ink weight for each color. Finally, the CPU 31 subtracts the quantity of used ink from the residual quantity of ink thus calculating the residual quantity of ink when printing is performed.