A connecting device is disclosed, which includes a connector structure having a housing, a plug connector, a plurality of electrical contacts and a magnetic-metal set. The housing has a surface on which the electrical contacts and the magnetic-metal set are disposed, and the plug connector protrudes from the housing and is electrically connected to the electrical contacts. An electronic device assembly is further disclosed, which includes an electronic device and the aforesaid connecting device. The connecting device can be inserted into a socket connector of the electronic device, so as to transform the socket connector into a non-pluggable magnetic connector.