To provide an image processor capable of indicating that an image does not have an effective range on a display device such as a plasma display panel performing under-scan display.

The PDP 100 which processes an image having an effective range for providing image data is equipped with an A/D converter 121 and a differential/parallel conversion part 126 for obtaining image data, a setting part 132 which sets one of a 1st mode in which the effective range 136 is displayed and a 2nd mode in which a part outside the effective range 136 is displayed, a generation part 133 which generates display data indicating the set display mode from the obtained image data, and a frame memory 124 which outputs the generated display data.