To enable simple and detailed confirmation of an operation instruction from an operation panel provided to a printer, each time an instruction is given using a preview button in the operation panel of the printer, an interruption event transferred from the printer to a host computer is detected, and in accordance with the detected interruption event, image data read out from a memory card attached to the printer, and a print setting to be set, are obtained. A preview display unit controls a print preview display reflecting the print setting in real time to a display device of the host computer, and also controls an update display of the print preview display.