An adapter mounting structure for mounting, on a rack, a plurality of adapters to which optical connectors are connected. The adapter mounting structure includes a first panel including insertion holes through which the plurality of adapters are inserted, the first panel being configured to expose, to a front side of the rack, the plurality of adapters thus inserted and being anchored to the rack, and a second panel disposed to a rear side of the rack relative to the first panel, the second panel being anchored to the first panel and being configured to anchor each of the plurality of adapters.