An inhibitor contains naphthyridine dimer, a naphthyridine-azaquinolone hybrid, a trinaphthyridine-azaquinolone hybrid, or a trinaphthyridine-azaquinolone hybrid derivative. In order to inhibit binding of 100 nM of RRE to 100 nM of Rev protein, for example, an inhibitor containing naphthyridine dimer is used at a molarity of 1.2 μM to 12 μM, an inhibitor containing the naphthyridine-azaquinolone hybrid is used at a molarity of 2 μM to 20 μM, or an inhibitor containing the trinaphthyridine-azaquinolone hybrid derivative is used at a molarity of 200 nM to 2 μM. This makes it possible to effectively inhibit binding of RRE to Rev protein.