The disclosure provides an accessory apparatus for an electronic device having a page-turning function, an electronic device and an electronic device assembly. The accessory apparatus comprises: a protective cover, which partially or completely wraps the electronic device and directly attaches to a back of the electronic device, wherein the protective cover is connected to an outer surface of the electronic device; a page-turning button, which is configured to perform a page-turning operation; a flexible printed circuit, which is provided with a page-turning triggering component, wherein the page-turning triggering component is in contact with the page-turning button and is configured to detect a page-turning instruction in response to the page-turning operation, and wherein the page-turning instruction is transmitted to the electronic device by the flexible printed circuit and a support member, which is configured to support the flexible printed circuit.