An adapter and a portable electronic device which may contain the adapter are disclosed. The adapter may be detachably contained in a containing recess of the portable electronic device, and it includes a base, a first connecting end and a second connecting end. The first connecting end is disposed on the base, and the second connecting end and the first connecting end are electrically connected to each other. In addition, a containing recess is formed on a surface of the portable electronic device for containing the adapter. The portable electronic device may remind the user to put away the adapter into the containing recess.