To provide a compact photocatalytic reaction apparatus in which OH radicals can be stably generated and which has such a structure that the packing ratio of a photocatalyst can be increased.

This photocatalytic reaction apparatus is provided with an introduction part 2 for introducing the exhaust gas containing a halogenated organic compound, a reaction part 3 in which the exhaust gas introduced from the introduction part 2 is brought into contact with the photocatalyst while being irradiated with the light emitted from light sources 3a-3d arranged inside the reaction part 3 to decompose the halogenated organic compound contained in the exhaust gas and a discharge part 4 for discharging the exhaust gas of which the halogenated organic compound is decomposed in the reaction part 3. A humidifying means 2a is arranged on a piping on the upstream side from the introduction part 2 for humidifying the exhaust gas.