A semiconductor device including a selection section that selects and outputs one video signal from plural input video signals; a clock signal output section that outputs a clock signal that corresponds to the video signal selected by the selection section; and a masking section that, for a predetermined period starting from a point when the clock signal output from the clock signal output section is switched in accordance with a switching of the selection of the video signal, performs masking processing on a synchronization signal that, among plural synchronization signals that correspond respectively to the plural video signals, corresponds to the video signal selected by the selection section. The selection section outputs the selected video signal in synchronization with the synchronization signal that corresponds to the selected video signal and that has undergone masking processing.