Abstract: A memory stores area specifying data for controlling a switch in the path of a signal of a first image in order to replace a portion of a first video signal with another signal (second video signal or the like). The control data of the memory can be obtained by converting a video signal, derived by use of a video camera, into a binary signal by a binary-coding circuit. In this case, a subject photographed by the video camera is a sheet of white rectangular paper on which an area edged or surrounded by a boarder line is specified, for example. In order to create the above area specifying data by photographing the subject on which the edged or surrounded area is specified, an edge counter, an odd/even number detection circuit, a flip-flop circuit, an AND circuit and a delay circuit are provided. That is, when an edge signal is supplied, the edge counter counts the edge signal and the odd/even number detection circuit and determines whether the counted value is odd or even.