To expand the spectral window for the light-induced charge separation in photosystem (PS) I of oxygenic photosynthetic organisms artificially, Rhodamine B (RhB) was covalently linked to the solution-exposed surfaces of PS I. By introduction of RhB to PS 1, the activity of light-induced charge separation for excitation wavelength at which the light absorption is dominated by RhB increased by about 1.8-fold, showing that RhB covalently attached to PS I can serve as the artificial light-harvesting antenna.