a photoelectric conversion apparatus includes a photoelectric conversion element and a logarithmic conversion unit for converting a signal from the photoelectric conversion element to a logarithmically compressed voltage by means of a diode characteristic of p - n junction . the p - n junction in the logarithmic conversion unit is composed of any two terminals of the emitter , the base and the collector of the bipolar transistor , and a residual terminal of the transistor is connected to a semiconductor substrate .