The invention provides a device for removing a harmful substance and an air cleaning device by utilizing the device for removing the harmful substance to clean air. According to the device for removing the harmful substance, a harmful gas component trapped by circulating water can be processed in high efficiency by oxidative decomposition and the production of harmful intermediate during the decomposition of the harmful gas component can be reduced substantially. The device for removing the harmful substance comprises: an ultraviolet ray-penetrable separation body (24), which is inside a cylindrical container main body (23) an air chamber (26), which is formed inside the separation body (24) an ultraviolet radiation lamp (30), which is inside the air chamber (26) a carrier-loading photocatalyst (2), which is inside a fluid bed (25) and fills the space between the container main body (23) and the separation body (24) an air pump (38), which is used to introduce the air into the air chamber (26) and an aerator pipe (42), which is used for aerating the air inside the air chamber (26) to the fluid bed (25). The device for removing the harmful substance enables the circulating water capable of trapping the harmful gas component to flow circularly through the fluid bed (25).
