A cable management device/arm is applied to a rack-mounted device system. Cables of a device are managed through a variable-length foldable cable management device/arm. In addition, when an electronic device is fully held in a rack, the cable management device/arm is held at a certain angle in the rack, the interference between the cable management device/arm and a power cable can be prevented from being produced and the length of the cable management device/arm can be flexibly adjusted according to specific application scenarios.