To allow a user to more easily view a video image of an outer area than a middle part by allowing the user to select a 1st or 2nd multi-screen display mode, displaying video images for all channels on a display area below a display available area of a monitor when the 1st multi-screen display mode is selected and displaying video images by all channels over the entire display area in the 2nd multi-screen display mode.

A user uses a multi-screen display mode changeover switch 23 to set a multi-screen display mode for the 1st multi-screen display mode in the case of utilizing a TV monitor on market for a supervisory monitor. When the user selects the 1st multi-screen display mode, a memory management section 33 controls a frame memory section 34 so that the frame memory section 34 stores only video data within a horizontal video image middle part smaller than a horizontal video signal valid area and within a vertical video image middle part smaller than a vertical video signal valid area. When the user selects the 2nd multi-screen display mode, the memory management section 33 controls the frame memory section 34 so that the frame memory section 34 stores the video data in the entire area.