This plant-cultivation illumination device (1) is provided with a first light source (2) for irradiating a plant (P) with a light that includes a red-colored light component, and a second light source (3) for irradiating the plant (P) with a light that includes a far-red-colored light component. The irradiation operation of the light source (2) is controlled by a control unit (4). A time slot in which the control unit (4) operates is set by a time setting unit (5). The time setting unit (5) performs the setting so that the first light source (2) implements the irradiation operation during a time slot straddling the sunset, and thereafter the second light source (3) implements the irradiation operation for three hours or longer during a time slot lasting until sunrise. This makes it possible to promote the growth of the plant (P), because the plant (P) is irradiated with a light that includes a red-colored light component during a time slot straddling the sunset and is thereafter irradiated with a light that includes a far-red-colored light component.
