PROBLEM TO BE SOLVED: To provide a photochemical reaction treatment device capable of controlling an unintended photoreaction due to an excess quantity of light by controlling the irradiation amount of light at a specified level and saving energy and maintenance time and labor. SOLUTION: This photochemical reaction treatment device is equipped with a plurality of light sources and performs a photochemical reaction treatment of an object to be irradiated with light from the light sources. In this device, some of the light sources are turned on or dimmed. Further, the irradiation is sequentially switched through combining the light sources to be turned on or dimmed. In addition, the dose of light to the object is controlled at a specified level by changing the ratio of the number of light sources to be turned on or dimmed to the number of light sources to be turned off with the elapse of time of using the light sources based on the illuminance deteriorating characteristics of the light source over time. Thus the unintended light reaction due to the excess quantity of light can be controlled.
