To provide an electrophotographic image forming device facilitating a locking operation even when a lock mechanism for a developing cartridge is provided in a position difficult to be accessed by a user.

This electrophotographic image forming device has a cartridge door 16 for opening and closing an opening part 40 for attaching and detaching the developing cartridge 5a, a lock member 18 for locking the developing cartridge 5a attached to an attaching part not to come off from attaching part, and turnable to release the lock, and a link member 20 abutting to the lock member 18, and turnable to switch between the lock and the lock releasing of the lock member 18, and an end part of the link member 20 is positioned in the vicinity of the opening part 40.

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