An irrigation device includes: a cell plug that includes an opening facing upward and an accommodation part that accommodates a predetermined amount of culture medium in communication with the opening; a liquid supply unit that supplies a liquid to a culture medium of the cell plug; and a cell plug lifting unit that lowers the cell plug when a weight of the cell plug is increased by a liquid supplied by the liquid supply unit and lifts the cell plug when a weight of the cell plug is decreased by drying of a culture medium. The liquid supply unit includes a contact end that is intermittently brought into contact with a culture medium by lifting and lowering of the cell plug by the cell plug lifting unit, performs liquid supply while the contact end is in contact with a culture medium, and stops liquid supply when the contact end is separated from a culture medium.