To provide a high voltage circuit for photodetector used in a photodetector for photometry which can be made compact while ensuring safety.

The high voltage circuit 10 for photodetector which supplies a high voltage power to a photomultiplier tube (PMT) 20 comprises a photovoltaic unit 11 configured by connecting multiple solar cells 11a electrically in series, and a light source 12 consisting of light-emitting diodes that emit light having a predetermined wavelength for the photovoltaic unit 11. Consequently, the high voltage circuit 10 can be made compact enough to be configured on a semiconductor, and high voltage power can be supplied stably and extremely easily to the PMT 20. Furthermore, since the light source 12 and the photovoltaic unit 11 generating a high voltage can be brought into so-called a photo-isolation state, the high voltage can be isolated extremely easily and reliably.