An optical fiber assembly (1a, 1b) comprising at least: an optical fiber; and a capillary having a through-hole in which the optical fiber is inserted, the optical fiber comprising: a core; and a clad which has a refractive index smaller than a refractive index of the core and which surrounds the core, wherein the optical fiber which has an element wire portion where a covering is removed and the element wire is exposed over a predetermined length from one end as the incidence end portion is inserted into the through-hole of the capillary, and one end as the incidence end portion of the optical fiber is protruded to an outside of the capillary, the optical fiber assembly (1a, 1b) further comprising: a fixing material (6a, 6b) fixing an outer periphery of the optical fiber and the capillary together; and a ceramic material (7a, 7b) disposed so as to be in contact with an entire outer circumference of the optical fiber where an adhesive of ceramic base material which is paste is coated thereon and to have a predetermined contact length in an axial direction of the optical fiber, wherein as viewed from the one end as the incidence end portion of the optical fiber, a position where the ceramic material (7a, 7b) is disposed is set in front of a position of the fixing material (6a, 6b) in contact with the outer periphery of the optical fiber and the core is protruded forward beyond the ceramic material (7a, 7b), characterized in that the refractive index of the ceramic material (7a, 7b) is set equal to or higher than the refractive index of the clad. an optical fiber; and a capillary having a through-hole in which the optical fiber is inserted, the optical fiber comprising: a core; and a clad which has a refractive index smaller than a refractive index of the core and which surrounds the core, wherein the optical fiber which has an element wire portion where a covering is removed and the element wire is exposed over a predetermined length from one end as the incidence end portion is inserted into the through-hole of the capillary, and one end as the incidence end portion of the optical fiber is protruded to an outside of the capillary, the optical fiber assembly (1a, 1b) further comprising: a fixing material (6a, 6b) fixing an outer periphery of the optical fiber and the capillary together; and a ceramic material (7a, 7b) disposed so as to be in contact with an entire outer circumference of the optical fiber where an adhesive of ceramic base material which is paste is coated thereon and to have a predetermined contact length in an axial direction of the optical fiber, wherein as viewed from the one end as the incidence end portion of the optical fiber, a position where the ceramic material (7a, 7b) is disposed is set in front of a position of the fixing material (6a, 6b) in contact with the outer periphery of the optical fiber and the core is protruded forward beyond the ceramic material (7a, 7b), characterized in that the refractive index of the ceramic material (7a, 7b) is set equal to or higher than the refractive index of the clad. a core; and a clad which has a refractive index smaller than a refractive index of the core and which surrounds the core, wherein the optical fiber which has an element wire portion where a covering is removed and the element wire is exposed over a predetermined length from one end as the incidence end portion is inserted into the through-hole of the capillary, and one end as the incidence end portion of the optical fiber is protruded to an outside of the capillary, the optical fiber assembly (1a, 1b) further comprising: a fixing material (6a, 6b) fixing an outer periphery of the optical fiber and the capillary together; and a ceramic material (7a, 7b) disposed so as to be in contact with an entire outer circumference of the optical fiber where an adhesive of ceramic base material which is paste is coated thereon and to have a predetermined contact length in an axial direction of the optical fiber, wherein as viewed from the one end as the incidence end portion of the optical fiber, a position where the ceramic material (7a, 7b) is disposed is set in front of a position of the fixing material (6a, 6b) in contact with the outer periphery of the optical fiber and the core is protruded forward beyond the ceramic material (7a, 7b), characterized in that the refractive index of the ceramic material (7a, 7b) is set equal to or higher than the refractive index of the clad. a fixing material (6a, 6b) fixing an outer periphery of the optical fiber and the capillary together; and a ceramic material (7a, 7b) disposed so as to be in contact with an entire outer circumference of the optical fiber where an adhesive of ceramic base material which is paste is coated thereon and to have a predetermined contact length in an axial direction of the optical fiber, wherein as viewed from the one end as the incidence end portion of the optical fiber, a position where the ceramic material (7a, 7b) is disposed is set in front of a position of the fixing material (6a, 6b) in contact with the outer periphery of the optical fiber and the core is protruded forward beyond the ceramic material (7a, 7b), characterized in that the refractive index of the ceramic material (7a, 7b) is set equal to or higher than the refractive index of the clad.