We　propose　a　scheme　for　the　reconstruction　of　a　cavity　field　state.　In　the　scheme　the　cavity　field　is　first　displaced　by　a　microwave　source,　and　then　is　placed　in　front　of　one　slit　of　the　two-slit　apparatus.　Ground　state　atoms　pass　through　the　apparatus,　hitting　upon　the　screen　far　away　from　the　two-slit　apparatus.　The　atom-field　interaction　is　dispersive.　The　contrast　of　interference　fringes　is　directly　related　to　the　Wigner　function　for　the　field　state.　The　scheme　can　be　easily　generalized　to　measure　the　Wigner　function　of　an　entangled　state　of　two　spatially　separated　single-mode　cavities.