Automatic zipper device for sheet member and method for producing sheet product

In the present invention, a sheet member is automatically joined on a molding drum. Provided is an automatic zipper device (1) comprising a pair of bevel gears (10) which bite and join joining ends of a plurality of sheet members (S) having magnet adsorptive metallic cords and wound around the periphery of a molding drum (D), wherein the device is provided with: an inclined portion following cylinder (12) which is attached to a lateral movement device (20) which moves laterally on the molding drum (D) so as to be laterally movable, and which adjusts the height of the bevel gears (10) corresponding to the inclined surface of the sheet member (S) to be joined; a clamping cylinder (13) which adjusts the degree of biting by the bevel gears (10); a guide magnet rollers (15(1), 15(2)) for introducing the sheet member (S); and a member contact position stabilizing magnet (15(3)) for maintaining the position of the sheet member (S) at a constant position so that the sheet member (S) to be joined can be brought into c