A device for assembling a camera module includes a base and a buffer layer. The camera module includes a flexible printed circuit board (FPCB), a lens module positioned on the FPCB, and a stiffener adhering to the FPCB, opposite to the lens module. The lens module includes a first stepped surface facing away from the FPCB. The base includes a supporting surface for supporting the FPCB and defines a holding groove in the supporting surface for holding the lens module. The holding groove forms a second stepped surface for supporting the first stepped surface. The buffer layer is positioned on the second stepped surface and is elastically compressed when the camera module is subjected to a hot pressing process, which secures the stiffener adhering to the FPCB, to provide relief against, and extend the duration of, various pressures applied to the camera module.