The disclosure relates to an optical connection device reducing a connection loss between an SCF and an MCF. The optical connection device includes plural relay fibers and a capillary having third and fourth end faces. Each relay fiber includes a first core of Δ1, a second core of Δ2, and a cladding of Δ3. The capillary includes a tapered portion with an outer diameter ratio R of the fourth end face to the third end face of 0.2 or less. In each relay fiber, a value of Formula (V2−V1)/R falls within a range from 156% μm2 to 177% μm2, V1 (% μm2) is given by (π·r1b2)×(Δ1−Δ2) by using a radius r1b (μm) of the first core, and V2 (% μm2) is given by (π·r2b2)×(Δ1−Δ2) by using a radius r2b (μm) of the second core.