A growth inhibitor of bacteria of the genus Legionella contains as an active ingredient a Macaranga tanarius extract extracted from Macaranga tanarius with an extraction solvent including at least an organic solvent. Alternatively, the growth inhibitor of bacteria of the genus Legionella contains as an active ingredient at least one selected from nymphaeol-.A, nymphaeol-B, and nymphaeol-C. The growth inhibitor of bacteria of the genus Legionella is used by being blended to, for example, a bath agent or a cleaning agent.