A photographic film cassette assembling method includes the steps of joining shell halves together by ultrasonic welding, to form a cassette shell, while accommodating a spool in the cassette shell. A film connection sheet is secured to the spool before the spool is mounted in the cassette shell. A free end of the film connection sheet is placed outside the cassette shell through a film passage mouth of the cassette shell. A strip of a photographic film is connected to the spool by attaching a trailing end of the photographic film to the free end of the film connection sheet and wound about the spool by rotating the spool. The photographic film may be directly secured to a spool having an engaging member formed therein and a film guide member formed integrally therewith. A free end or free ends of the guide member protrude slightly from the film passage mouth to the outside of the cassette shell. The trailing end of the photographic film is guided along the film guide member into the cassette shell toward the engaging member of the spool, thereby to bring the end of the photographic film into engagement with the engaging member.