Abstract: An apparatus of the present invention is an apparatus for housing a splice reinforcing portion of optical fiber, which comprises (a) a first holding member for holding a splice reinforcing portion for reinforcing a splice between a first optical fiber and a second optical fiber optically connected to the first optical fiber and constituting a light transmission line together with the first optical fiber, and (b) a first photosensor disposed on a side surface of the splice reinforcing portion, receiving leaking light from the splice reinforcing portion, and fixed to the first holding member.