An interference filter module comprising: a first optical fiber collimator and a second optical fiber collimator, which have a fore-and-aft direction as a direction of an optical axis and are arranged at a front end and a rear end of a casing so as to be located on said optical axis and opposed to each other; and 2n interference filters (5a, 5b) arranged inside said casing so as to be located on said optical axis where n is a natural number, wherein, said casing includes: a main body portion; and 2n filter holding portions (4a, 4b), each being configured to hold a corresponding one of said interference filters (5a, 5b), which are to be mounted into said main body portion, each of said interference filters (5a, 5b) includes a substrate (54a, 54b) and an interference film (55a, 55b) laminated on said substrate (54a, 54b), when k is a natural number equal to or smaller than n, two interference filters (5a, 5b) including a k-th interference filter when counted from said front end toward said rear end of said casing and a k-th interference filter when counted from said rear end toward said front end of said casing are determined as a k-th set among said 2n interference filters, said two interference filters (5a, 5b) of said k-th set are respectively accommodated in one of said filter holding portions, which is a k-th filter holding portion when counted from said front end toward said rear end of said casing, and in another one of said filter holding portions, which is a k-th filter holding portion when counted from said rear end toward said front end of said casing, and said two filter holding portions (4a, 4b) corresponding to said k-th filter holding portion when counted from said front end of said casing and said k-th filter holding portion when counted from said rear end of said casing are held rotatably in said casing; characterized in that: said main body portion has a cylindrical shape; said two filter holding portions (4a, 4b) corresponding to said k-th filter holding portion when counted from said front end of said casing and said k-th filter holding portion when counted from said rear end of said casing have rotation axes in directions orthogonal to said fore-and-aft direction; and said rotation axes of said two filter holding portions (4a, 4b) are orthogonal to each other. a first optical fiber collimator and a second optical fiber collimator, which have a fore-and-aft direction as a direction of an optical axis and are arranged at a front end and a rear end of a casing so as to be located on said optical axis and opposed to each other; and 2n interference filters (5a, 5b) arranged inside said casing so as to be located on said optical axis where n is a natural number, wherein, said casing includes: a main body portion; and 2n filter holding portions (4a, 4b), each being configured to hold a corresponding one of said interference filters (5a, 5b), which are to be mounted into said main body portion, a main body portion; and 2n filter holding portions (4a, 4b), each being configured to hold a corresponding one of said interference filters (5a, 5b), which are to be mounted into said main body portion, each of said interference filters (5a, 5b) includes a substrate (54a, 54b) and an interference film (55a, 55b) laminated on said substrate (54a, 54b), when k is a natural number equal to or smaller than n, two interference filters (5a, 5b) including a k-th interference filter when counted from said front end toward said rear end of said casing and a k-th interference filter when counted from said rear end toward said front end of said casing are determined as a k-th set among said 2n interference filters, said two interference filters (5a, 5b) of said k-th set are respectively accommodated in one of said filter holding portions, which is a k-th filter holding portion when counted from said front end toward said rear end of said casing, and in another one of said filter holding portions, which is a k-th filter holding portion when counted from said rear end toward said front end of said casing, and said two filter holding portions (4a, 4b) corresponding to said k-th filter holding portion when counted from said front end of said casing and said k-th filter holding portion when counted from said rear end of said casing are held rotatably in said casing; characterized in that: said main body portion has a cylindrical shape; said two filter holding portions (4a, 4b) corresponding to said k-th filter holding portion when counted from said front end of said casing and said k-th filter holding portion when counted from said rear end of said casing have rotation axes in directions orthogonal to said fore-and-aft direction; and said rotation axes of said two filter holding portions (4a, 4b) are orthogonal to each other. said main body portion has a cylindrical shape; said two filter holding portions (4a, 4b) corresponding to said k-th filter holding portion when counted from said front end of said casing and said k-th filter holding portion when counted from said rear end of said casing have rotation axes in directions orthogonal to said fore-and-aft direction; and said rotation axes of said two filter holding portions (4a, 4b) are orthogonal to each other.