In an apparatus for producing a tubular body with a membrane forming a separating wall extending across the interior of the tubular body, an injection mold is provided including a cylindrical hollow space corresponding to the outer wall of the tubular body and a pin is disposed in the cylindrical chamber in spaced relationship with the wall thereof so as to form a tubular passage, wherein the pin includes upper and lower parts which are movable relative to each other so as to form an adjustable gap between which is in communication circumferentially with the tubular passage.