In an initial state, a key control switch for adjusting opening degrees of ink keys and a display changeover switch are displayed on a display screen of a touch sensitive control panel. The key control switch is a collection of key control switches individually arranged in areas corresponding to the ink keys, and for each ink color. The individual key control switches indicate color densities of control strips on a print measured by a color density measuring device and the opening degrees of the ink keys. When the changeover switch is operated in this state, the control panel simultaneously displays the key control switches and an image of the print being processed.