A gas concentration measurement device includes a waveguide including an entrance and an exit, a rotating member, first and second band pass filters on the rotating member and on a pair of planes that intersect each other, and a rotational driver. The rotating member is rotated by the rotational driver so that the first and second band pass filters are selectively located at a transmitting position. When a portion of the rotating member, the first band pass filter, or the second band pass filter, the portion having a maximum radius of gyration around a rotating shaft, is defined as a maximum radius portion, and when a rotation locus obtained by imaginarily rotating the maximum radius portion around the rotating shaft in a view along the rotating shaft is defined as a reference circle, the exit is located in the reference circle.