A filter holding apparatus holding a first chemical filter and a second chemical filter, includes a first frame which holds the first chemical filter and which has a first guide groove provided on a side surface of the first frame; a second frame which holds the second chemical filter and which has a second guide groove provided on a side surface of the second frame and which is arranged while being overlapped with the first frame; and each of the first and second guide grooves has a first groove which is communicated with a back surface of one of the first and second frames, and a second groove which is communicated with the first groove and which extends toward an upper end of one of the first and second frames; wherein a distance between the second groove and the back surface in the first frame is different from a distance between the second groove and the back surface in the second frame. A plurality of filters can be installed or exchanged efficiently and in such a manner that the filters are positioned easily.