To provide an apparatus easy to elongate a web formed of a thermoplastic synthetic resin over its whole width.

The apparatus 2 for elongating a web 1 formed of a thermoplastic synthetic resin has the following construction: A plurality of first web-elongating members L arranged circumferentially are provided on the circumferential surface of a drum 6 revolving in the machine direction M. The revolving shaft 8 of the drum 6 is provided with a rotator 7 rotating in the same direction of the drum 6 synchronously with the drum 6. The rotator 7 is provided with a plurality of second web-elongating members U corresponding to the first web-elongating members L, respectively. Each of the first web-elongating members L and each of the second web-elongating members U corresponding to each other is such that sites standing against each other in the radial direction of the drum 6 are in the form of projections 31 and 41 and recesses 32 and 42, respectively, extending in parallel to the shaft 8 and arranged alternately in the circumferential direction of the drum 6, having a complementary shape as to be detachably engaged with each other in the radial direction of the drum 6. The first web-elongating members L and/or the second web-elongating members U are formed to be movable in the radial direction of the drum 6.