An ice maker of the present invention comprises: an upper tray defining an upper chamber that is a portion of an ice chamber, wherein an upper opening is provided in an upper side of the upper tray; a lower tray defining a lower chamber that is another portion of the ice chamber; a lower support supporting the lower tray and provided with a lower heater; and a control unit configured to operate the lower heater in an ice making process, wherein the control unit variably controls an output of the lower heater so that bubbles included in water in the ice chamber are gathered in a lowermost section in the ice making process.