A semiconductor photodetector device includes a light receiving operation section converting incident light to an electric signal and a current amplifying operation section amplifying the electric signal. The light receiving operation section includes: a first conductivity type semiconductor layer a formed on a first conductivity type semiconductor substrate; a second conductivity type first semiconductor region formed on the semiconductor layer; and a first conductivity type second semiconductor region formed on the semiconductor layer and separated from the first semiconductor region. The current amplifying operation section includes: the second semiconductor region; a second conductivity type third semiconductor region formed in the semiconductor substrate; a second conductivity type fourth semiconductor region formed on the third semiconductor region and separated from the second semiconductor region.