PURPOSE: To enable to generate high photocurrent with faint light and a small photo receiving area by optical exposure of part of the first impurity region.

CONSTITUTION: The light L of the invisible region generates holes and electrons in silicon. The electrons generated in a photo irradiated region 16 by irradiation of the optically exposed region 16 of the first impurity region 12 with the light L are collected to the plus charged second impurity region 13, and the holes flow to a semiconductor substrate 11. The holes flowing into this substrate 11 are amplified, and the inflow of electrons generates from the substrate 11 to the impurity region 12 and is further collected to the impurity region 13. The charges of the region 13 are rapidly discharged, and the discharged charges are charged from the third impurity region 14 by application of readout pulses on a gate electrode 15 at the time of readout of this photo charge. Then, this charged charge is observed as the photo signal.