Scroll fluid machine including back-pressure chamber with increased pressure receiving area

A scroll fluid machine comprising:

• a casing;
• a fixed scroll member provided to said casing, said fixed scroll member having an end plate and a spiral wrap portion standing on a surface of said end plate;
• a rotating shaft supported by said casing and driven to rotate by a drive source;
• an orbiting scroll member provided to face said fixed scroll member, said orbiting scroll member having an end plate and a spiral wrap portion standing on a surface of said end plate so as to overlap the wrap portion of said fixed scroll member to define a plurality of compression chambers therebetween;
• a back-pressure chamber forming member integrally provided with said casing at a back of said orbiting scroll member to form a back-pressure chamber between itself and the back of said orbiting scroll member said back-pressure chamber being in communication with said compression chambers;
• a coupling member integrally provided with said orbiting scroll member with said back-pressure chamber forming member interposed therebetween, said coupling member being coupled to said rotating shaft through an orbiting bearing;
• and
• a rotation preventing mechanism that prevents said orbiting scroll member and coupling member from rotating around their axis.