A semiconductor integrated circuit includes a clock-signal control circuit controlling intensity-signal output, which is output from a signal processing circuit, to be stopped in at least a forward outage time and a backward outage time. The forward outage time is previous to an apex point of a triangular wave and having 1 to 5% of a triangular wave period. The backward outage time is subsequent to the apex point of the triangular wave and having 1 to 5% of a triangular wave period.