A motion-picture camera having exposure and sound-recording structures past which the film is transported by a pair of film-transporting structures, respectively, at least one of which is driven by a variable speed electric motor. The film is transported both forwardly and rearwardly and forms between the exposure and sound-recording structures a loop from which the film is continuously transported to the sound-recording structure and to which the film is transported in a stepwise manner from the exposure structure. A detecting device detects when this film loop becomes longer or shorter than a predetermined magnitude, and through a suitable circuit this detecting device is connected with the variable speed motor for controlling the speed thereof so as to increase the length of the film loop when it becomes shorter than the predetermined magnitude and decrease the length of the film loop when it becomes longer than the predetermined magnitude, so that in this way the film loop is maintained at the predetermined magnitude. The components referred to above operate both during forward as well as rearward travel of the film so that it is necessary to displace components of the sound-recording structure away from the film during rearward travel of the latter.