The present invention is intended to make it possible to form patches that allow for a high precision measurement of a threshold of an electric energy to be supplied to nozzles of a print head, without using a high-precision sensor. To this end, this invention changes the electric energy supplied to the nozzles of the print head stepwise in printing patches that are used to measure an ink droplet ejection state of the nozzles for each level of electric energy. The patch printing involves dividing the nozzle column of the print head into a plurality of nozzle groups and scanning at least one of the nozzle groups a plurality of times over each of the plurality of patch forming areas set on a print medium.