To provide a simple disinfection device in a water circulating compressor line that perfectly disinfecting bacteria in compressed air supplied from the water circulating compressor line to a using side.

In order to disinfect bacteria in a compressed air supplied from a water circulating compressor line composed of a compressor body 6, a receiver tank 7, a cooling means 10 and the like to a using side 9, and moisture included in the compressed air, a disinfecting means 1, for example, using ultraviolet and the like is provided in a middle point of a feed pipe 15 connecting the receiver tank 7 and the using side 9. Therefore, the bacteria in the compressed air is supplied to the using side 9 while being completely disinfected.