PROBLEM TO BE SOLVED: To stretch a polymer film while suppressing breaking of the film. SOLUTION: An off-line stretching apparatus includes a housing chamber and a tenter. The housing chamber houses a preceding film roll and a succeeding film roll. The tenter holds a preceding film sent out of the preceding film roll and widens the preceding film. After all preceding films are sent out, a succeeding film is sent out of the succeeding film roll to the tenter. At a joint provided before the tenter, a rear end 3ax of the preceding film 3a and a top end 3bx of the succeeding film 3b are superposed to provide an overlapping 60. The overlapping 60 is held by a horn 66 vibrating in a C direction and a receiving surface 55 and welding processing is performed. The tenter widens the film which is subjected to the welding processing. COPYRIGHT: (C)2011,JPO&INPIT