An interplay between the superconductivity and the antiferromagnetic (AFM) ordering in the heavy-fermion materials such as UPd 2 Al 3 is examined using a spin density wave picture. The experiments suggest coexistence of two kinds of only weakly coupled 5f-electrons in the U atom, an itinerant one and a localized one. As a first approximation, a direct coupling between them is ignored. The fluctuation around the mean-field state is considered to be an origin of the AFM interaction of the localized f-electron. When the conduction electron becomes superconducting, it affects the fluctuation process by smearing out a sharp boundary of the Fermi distribution. This explains a gradual decrease of the AFM moment of the localized f-electron observed at T < T c .