An ice maker of a refrigerator includes a tray assembly having an upper tray that defines upper portions of a plurality of ice making chambers. Each of the plurality of ice making chambers is configured to receive water and generate an ice piece. The tray assembly also includes a lower tray that is located vertically below the upper tray, that is configured to rotate relative to the upper tray, and that defines lower portions of the plurality of ice making chambers, wherein at least one of the upper tray or the lower tray comprises a flexible tray made of a flexible material. Additionally, a case is configured to accommodate the flexible tray to restrict a deformation of the flexible tray. A heater that is located between the case and the flexible tray is configured to supply heat to the plurality of ice making chambers through the flexible tray.