An aseptic filling system comprising: a heat sterilizer that sterilizes a content by heat; and a filling machine that fills a bottle with the content sterilized by heat by the heat sterilizer; wherein: the heat sterilizer includes a heating unit that heats the content, and a cooling unit that cools the content heated by the heating unit; a circulation line that circulates aseptic water is connected between the heating unit and the cooling unit, characterised in that the circulation line includes a heating-water line that supplies the heating unit with heating water from the cooling unit, and a cooling-water line that supplies the cooling unit with cooling water from the heating unit; wherein the heating-water line and the cooling-water line constitute a sealed circulation line closed to the outside; the hot water which has cooled the content at the cooling unit is supplied into the heating unit through the heating-water line, and heats the content at the heating unit, and, the cooling water which has heated the content at the heating unit is supplied into the cooling unit through the cooling-water line, and cools the content at the cooling unit, and the cooling-water line is provided with a connection line that supplies aseptic water to the filling machine. a heat sterilizer that sterilizes a content by heat; and a filling machine that fills a bottle with the content sterilized by heat by the heat sterilizer; wherein: the heat sterilizer includes a heating unit that heats the content, and a cooling unit that cools the content heated by the heating unit; a circulation line that circulates aseptic water is connected between the heating unit and the cooling unit, characterised in that the circulation line includes a heating-water line that supplies the heating unit with heating water from the cooling unit, and a cooling-water line that supplies the cooling unit with cooling water from the heating unit; wherein the heating-water line and the cooling-water line constitute a sealed circulation line closed to the outside; the hot water which has cooled the content at the cooling unit is supplied into the heating unit through the heating-water line, and heats the content at the heating unit, and, the cooling water which has heated the content at the heating unit is supplied into the cooling unit through the cooling-water line, and cools the content at the cooling unit, and the cooling-water line is provided with a connection line that supplies aseptic water to the filling machine. the heat sterilizer includes a heating unit that heats the content, and a cooling unit that cools the content heated by the heating unit; a circulation line that circulates aseptic water is connected between the heating unit and the cooling unit, characterised in that the circulation line includes a heating-water line that supplies the heating unit with heating water from the cooling unit, and a cooling-water line that supplies the cooling unit with cooling water from the heating unit; wherein the heating-water line and the cooling-water line constitute a sealed circulation line closed to the outside; the hot water which has cooled the content at the cooling unit is supplied into the heating unit through the heating-water line, and heats the content at the heating unit, and, the cooling water which has heated the content at the heating unit is supplied into the cooling unit through the cooling-water line, and cools the content at the cooling unit, and the cooling-water line is provided with a connection line that supplies aseptic water to the filling machine.