PROBLEM TO BE SOLVED: To provide an automatic sealing device capable of positioning a bag mouth to be sealed relative to a sealing machine even when a packaging bag is fed easily in a manual or mechanical manner. SOLUTION: Two conveyor belts 33, 34 are arranged in V-shape as a carrying machine 11 to carry a packaging bag X. When the packaging bag X is feed on the belts 33, 34, a lower end part of the bag X is abutted on one belt 34 by the self-weight of the bag, and a side part of the bag is abutted on the other belt 33 in a natural posture. A bag mouth at the upper end part of the packaging bag X can be positioned contact relative to a pressing base 61 or a heating base 62 of a sealing machine 41, and the defective seal can be avoided.