PROBLEM TO BE SOLVED: To assist an exact and rapid offside decision by rapidly presenting the video on an offside line when the offside decision is carried out. SOLUTION: A driver 12 is controlled by a controller 13, by which the position of an imaging device 11 is controlled and the video on the offside line is picked up. On the other hand, the time when the offside decision is carried out is instructed by an image acquisition instruction input device 4 and the video on the offside line picked up by the imaging device 11 at this time is sent as an image from an image transmitter 21. The image on the offside line received by an image receiver 31 is displayed by an image display device 32.
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