Video picture signals are received via at least three channels. At least three control instructing operators are provided in correspondence with the channels. Each control instructing operator is operable to give a signal control instruction for the corresponding channel in accordance with an operated amount of the operator. Controller performs signal control on the video picture signals of the channels on the basis of the respective signal control instructions given via the control instructing operators. Synthesizer synthesizes the video picture signals of the channels having been subjected to the signal control by the controller. Video picture signals of two desired channels are designated, and a contact-type operator gives signal control instructions, corresponding to a predetermined position of the operator contacted by a human operator, with respect to the video picture signals of the designated two channels. By the signal control instructions, signal control is performed on the video picture signals of the designated two channels to thereby synthesize the video picture signals.