A stretching apparatus for thermoplastic synthetic resin improved so as to ensure that a web can be easily stretched over its entire width. The stretching apparatus 2 for a thermoplastic synthetic resin web 1 comprises a plurality of first stretching members L arranged in a circumferential direction on a peripheral surface of a drum 6 rotating in a machine direction M. The drum 6 is provided around its rotating shaft 8 with rotatable members 7 adapted to rotate in synchronization with the drum 6 in the direction in which the drum 6 rotates. The rotatable members 7 are respectively provided with a plurality of second stretching members U operatively associated with the first stretching members U. Surfaces of the first and second stretching members L, U associated with each other are defined by convex portions 31, 41 and concave portions 32, 42 extending in parallel to the shaft 8 and alternately arranged in the circumferential direction of the drum 6 in a complementary fashion to each other so that these surfaces of the first and second stretching members L, U configured in this manner may be engaged with and disengaged from each other. At least one of the first stretching member L and the second stretching member U is movable in the radial direction of the drum 6.