PROBLEM TO BE SOLVED: To provide a backflow prevention valve assembly in which the thickness of a portion having a backflow prevention valve can be reduced, and which can be easily mounted and replaced. SOLUTION: This valve comprises an upper lid 20, a backflow prevention valve 30, and a valve receiving member 40. The backflow prevention valve 40 comprises a main body 31 having a slit 33 at a lower end 31b and a flange 34, and a valve receiving member. 40 comprises an annular flat plate 41 having an opening at the center, the check valve 30 has a flange portion 34 sandwiched between the upper lid 20 and the annular flat plate 41, and a main body portion 31 protruding downward from the opening of the valve receiving member 40. The check valve assembly 10 has a check valve. [Selection diagram] Fig. 3【課題】逆流防止弁を有する部分の厚さを薄くすることが可能であり、装着及び交換が簡便な逆流防止弁組立体を提供することを目的とする。【解決手段】上蓋２０と、逆流防止弁３０と、弁受け部材４０とから構成され、逆流防止弁４０が、下端３１ｂにスリット３３を有する本体部３１とフランジ部３４とからなり、弁受け部材４０が、中央に開口を有する環状平板４１からなり、逆流防止弁３０は、フランジ部３４が上蓋２０と環状平板４１とで挟持され、本体部３１が弁受け部材４０の開口から下方に突出している逆流防止弁組立体１０とする。【選択図】図３
