An assembling device for assembling an actuator and a lens module. The actuator includes a first top surface for supporting the lens module and a first bottom surface. The lens module includes a top portion for receiving lens and a bottom portion. The diameter of bottom portion is slightly larger than the top portion. The bottom portion further includes a second first bottom surface in contact with the first top surface. The assembling device includes a base, a support set, and a pressing sheet. The base includes a supporting surface for supporting the first bottom surface. The support set is above the base and defines at least three threaded holes therethrough. The pressing sheet is in contact with the second top surface. The at least three pins are movably threaded with the threaded holes correspondingly and configured for pushing the pressing sheet.