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　couples　with　a　three-level　Lambda　-type　atom　in　a　Raman　manner.　After　an　appropriate　interaction　time　the　measurement　of　the　difference　between　the　probabilities　of　the　atom　being　in　two　ground　states　directly　yields　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.