A gas purification apparatus capable of removing fine particles of substantially any size without lowering the efficiency of gas supply. A loader module of a substrate processing apparatus includes a fan filter unit for producing a downward flow of atmospheric air in the internal space of a transfer chamber. The fan filter unit includes a fan for generating an atmospheric air flow, a filter of mesh structure for trapping and removing particles mixed in the atmospheric air flow, an irradiation heater disposed between the fan and the filter, and a high temperature part disposed in the atmospheric air flow and higher in temperature than the filter.