To provide a photometric detector having a wide dynamic range which can cope with a wide analysis up to a high concentration sample from a low concentration sample.

A photometric detector is provided with a high voltage power source part 10 to impress high voltage on a negative electrode of a photomultiplier 8 and an amplifier 9 to amplify and output an electric signal converted by the photomultiplier 8, and the high voltage to be impressed on the negative electrode of the photomultiplier 8 from the high voltage power source part 10 is changed so that output of the amplifier 9 is kept constant. That is, in the case of a high concentration sample, the high voltage impressed on the negative electrode of the photomultiplier 8 from the high voltage power source part 10 becomes low, and to the contrary, in the case of a low concentration sample, its high voltage is controlled so that the voltage becomes high. The high voltage to be impressed on the negative electrode of the photomultiplier 8 from the high voltage power source part 10 is found by calculation on the basis of a prestored sensitivity characteristic of the photomultiplier 8 in order to keep output of the amplifier 9 constant.