An image processor includes a parking area line detection portion configured to detect a parking area line from an image acquired by an imaging device, a parking frame setting portion configured to set a parking frame based on the detected parking area line, a parking frame selection portion configured to calculate a length ratio of adjacent first and second sides of the set parking frame, determine the parking frame as a display target when the length ratio falls within a predetermined range, and not to determine the parking frame as the display target when the length ratio falls outside the predetermined range, and a display control portion configured to control a display portion for displaying a parking frame image showing the parking frame determined as the display target by the parking frame selection portion so as to keep superimposing the parking frame image onto the image.