A blow molding device is provided with a mold in which a preform is disposed, a cylindrical nozzle that is inserted into a mouth part of the preform, a pressurized fluid supply part for supplying a pressurized incompressible fluid to the nozzle, a sealing body that is movable between a closed position that blocks the nozzle and an open position that opens the nozzle, a plurality of suction holes provided on an inner peripheral surface of the nozzle, a vertical hole provided extending along the axial direction of the nozzle for connecting a plurality of suction holes to each other, and a suction pump connected to the vertical hole via a suction path for applying suction force to a plurality of the suction holes for suctioning incompressible fluid adhered to the nozzle.