The plant growth promoting device includes a container that contains a culture solution of a cultivated plant, a counter electrode group that is disposed opposite to the container and has a plurality of electrodes, a power source that applies a voltage between the counter electrode groups, and an ammeter A measuring device that measures a current value between the pair of electrode groups and a voltage application control section that applies a voltage between the partial electrodes of the plurality of electrodes, and determines, based on the partial electrode to which the voltage is applied And determines the presence or absence of a root of the plant, and applies a voltage for promoting growth in the presence of the root of the plant.
