A structure for transmitting a driving force from a camera body side to a cartridge chamber cover side in order to automatically operate a safety mechanism section of a safety locking mechanism installed inside the cover. The safety locking mechanism includes a locking mechanism section for locking the cover relative to the camera body; an unlocking operation member for manually releasing the locking mechanism section; and a safety mechanism section for selectively prohibiting or permitting the operation of the unlocking operation member. The driving force for automatically operating the safety mechanism section is transmitted from the camera body to the safety mechanism section through a winding spool of a film cartridge loaded inside the camera body.