An image printing apparatus is capable of printing an image at various resolutions, such as 300- and 360-dpi systems. To drive a printhead at a printing position corresponding to the resolution of printing data, information on whether to discharge ink separately in the forward and return passes of the printhead is stored in the storage area of a RAM in advance in correspondence with the main scanning position of the printhead. Data (0 or 1) stored in the RAM is read out by using, as a RAM address input, a count value output from a printhead position detection unit that represents the current position of the printhead. Only when the readout data is 1, a printing position pulse is generated to print an image at an arbitrary resolution. By setting ink discharge positions separately in the forward and return passes, an image can be printed at a high precision.