To suppress variation of a signal in a semiconductor device. By suppressing the variation, formation of a stripe pattern in displaying an image on a semiconductor device can be suppressed, for example. A distance between two adjacent signal lines which go into a floating state in different periods (G1) is longer than a distance between two adjacent signal lines which go into a floating state in the same period (G0, G2). Consequently, variation in potential of a signal line due to capacitive coupling can be suppressed. For example, in the case where the signal line is a source signal line in an active matrix display device, formation of a stripe pattern in a displayed image can be suppressed.