An assembly device includes a bottom base, two baffles, two screws, and two magnetic members. The bottom base includes a receiving portion configured to receive a camera module. The receiving portion includes two adjacent fixed members and two adjacent moveable members. The baffle is secured to a sidewall of the bottom base. The screw passes through one baffle and can push one moveable member. The magnetic member is arranged on one moveable member. When the screw is rotated toward a first direction, the one screw pushes the corresponding moveable member to move toward the opposite fixed member, when the one screw is rotated toward a second direction, the attraction between the one screw and the first magnetic member draws the corresponding moveable member away from the opposite fixed member.