An arrangement for detecting local light irradiation in an illegal attack attempt to intentionally induce a malfunction or faulty condition is formed on a small chip occupancy area so as to provide high detection sensitivity. In a region containing a logic circuit, a plurality of series-coupled detection inverters are distributively disposed as photodetector elements having a constant logical value of primary-stage input. When at least one of the series-coupled detection inverters is irradiated with light, an output thereof is inverted, thereby producing a final output through the series-coupled detection inverters. Based on the final output thus produced, local light irradiation can be detected.