Abstract: An optical fiber feedthrough includes a tubular-shaped sleeve and an elastic tube. The sleeve includes a through hole extending in an axial direction and is mountable to a package such that an end portion thereof on one side is located on an inner side of the package and an end portion thereof on an other side is located on an outer side of the package. The elastic tube includes an insertion portion entering the inside of the through hole from an outer end portion being an end portion on the other side of the through hole, and a projection portion projecting to the outside from the outer end portion. An optical fiber is insertable into the through hole and the elastic tube, and an outer peripheral surface of the elastic tube and an inner peripheral surface of the through hole are fixed to each other with an adhesive.