To provide a method for producing a polarizing film for sequentially and continuously producing a polarizing film, surely bonding the rear end part of a fed roll film with the front end part of the next roll film, and preventing breakage of in a heat seal part between the roll films.

In this method for producing a polarizing film, while continuously feeding a polyvinyl alcohol roll film wound in a roll, the roll film is extended in the longitudinal direction in a movement course, and at the same time, the rear end part of the fed roll film and the front end part of the next roll film are bonded together, so that a polarizing film is continuously produced. The bonding is carried out by putting the rear end part of the roll film and the front end part of the next roll film together and heat-welding them mutually at 200-300C.