To print a correction pattern capable of easily detecting an error at a time of the formation of a head shading data by forming correction data correcting printing irregularity due to a printing head on the basis of image data read by a reading means.

Four head correction patterns 801 to which printing region inspecting marks 802 and nozzle numbers 803 are applied with respect to respective colors are printed in order to detect the density irregularity of the printing image of a color bar code label printer. A head shading chart is read by a reading device and regions of head correction pattern parts are extracted and the density average (raster average of respective pixel rows in a paper feed, direction is calculated to be inputted to a temporary buffer. The addresses of the start and completion of a nozzle position are detected by utilizing the sudden change of an edge part and the raster average data from a start address is successively substituted for the buffer up to a completion address over again to take the correspondence of the stored data in the buffer and a nozzle.