A assembly apparatus for attaching decorative pieces to electronic devices includes a seat, a first cover, a second cover, and a transmitting member. The seat includes a disengaging portion and an attaching portion. The disengaging portion has a recess, a protrusion and at least one positioning column in the recess. The attaching portion defines a receiving room for receiving a shell. The first cover is detachable mounted on the disengaging portion and defines at least one first through hole. The second cover is detachable mounted on the attaching portion and defines a second through hole. The transmitting member includes a latching portion. The latching portion is inserted in the first through hole to attract a decorative piece, and is inserted in the second through hole to release the decorative piece on the shell.