An optical fiber-type optical filter (10, 20, 30, 40, 50, 60) comprising: two fiber regions (15a, 15b), each of which includes: a core section extending in a waveguide direction of incident light; and a clad section extending in the waveguide direction and surrounding the core section, the optical fiber-type optical filter (10, 20, 30,40, 50, 60) being characterized in that: the two fiber regions (15a, 15b) have identical optical fiber structures, the clad section includes a plurality of high refractive-index sections which have a refractive index higher than that of a base material of the clad section, extend in the waveguide direction, and are arranged periodically in a cross section perpendicular to the waveguide direction; the optical fiber-type optical filter (10, 20, 30,40, 50, 60) comprises: a light loss region (16, 16a, 16b, 16c, 16d) between mutually-facing end surfaces of the two fiber regions (15a, 15b), for coupling a radiation mode with a waveguide mode in which light intensity is observed in the high refractive-index sections in the clad section; and the light loss region (16, 16b, 16d) is a region constituted by an optical fiber which includes a core section extending in the waveguide direction and a clad section extending in the waveguide direction and surrounding the core section, and which is different from the two fiber regions (15a, 15b) at least in terms of a refractive-index distribution of the clad section. two fiber regions (15a, 15b), each of which includes: a core section extending in a waveguide direction of incident light; and a clad section extending in the waveguide direction and surrounding the core section, a core section extending in a waveguide direction of incident light; and a clad section extending in the waveguide direction and surrounding the core section, the two fiber regions (15a, 15b) have identical optical fiber structures, the clad section includes a plurality of high refractive-index sections which have a refractive index higher than that of a base material of the clad section, extend in the waveguide direction, and are arranged periodically in a cross section perpendicular to the waveguide direction; the optical fiber-type optical filter (10, 20, 30,40, 50, 60) comprises: a light loss region (16, 16a, 16b, 16c, 16d) between mutually-facing end surfaces of the two fiber regions (15a, 15b), for coupling a radiation mode with a waveguide mode in which light intensity is observed in the high refractive-index sections in the clad section; and the light loss region (16, 16b, 16d) is a region constituted by an optical fiber which includes a core section extending in the waveguide direction and a clad section extending in the waveguide direction and surrounding the core section, and which is different from the two fiber regions (15a, 15b) at least in terms of a refractive-index distribution of the clad section. a light loss region (16, 16a, 16b, 16c, 16d) between mutually-facing end surfaces of the two fiber regions (15a, 15b), for coupling a radiation mode with a waveguide mode in which light intensity is observed in the high refractive-index sections in the clad section; and the light loss region (16, 16b, 16d) is a region constituted by an optical fiber which includes a core section extending in the waveguide direction and a clad section extending in the waveguide direction and surrounding the core section, and which is different from the two fiber regions (15a, 15b) at least in terms of a refractive-index distribution of the clad section.