A suspension system for a vehicle, comprising: a fluid circuit (76; 281; 380) including (a) at least one fluid cylinder (30, 60; 180; 210, 212, 226, 228) provided on each of a front-wheel side and a rear-wheel side of the vehicle, each of said at least one fluid cylinder including a housing (36, 66; 182; 230), and a piton (38, 68; 194; 236) which separates an interior space of the housing into two fluid chambers (80, 82, 84, 86; 232, 234), said each fluid cylinder being disposed between a wheel-side member (10, 12, 20, 50; 204, 206, 224) of the vehicle and a body-side member of the vehicle, such that there arises a difference between fluid pressures in said two fluid chambers when at least one of a left wheel (24, 54; 202, 222) and a right wheel (24, 54; 200, 220) is displaced in a vertical direction relative to a body of the vehicle, and (b) two fluid passage systems (72, 74; 250, 252; 350, 352) one (72; 250; 350) of which connects one (80; 232) of the two fluid chambers (80, 84; 232, 234) of said at least one fluid cylinder on said front-wheel side to a corresponding one (82; 232) of the two fluid chambers (82, 86; 232, 234) of said at least one fluid cylinder on said rear-wheel side, and the other (74; 252; 352) of which connects the other (84; 234) of the two fluid chambers of said at least one fluid cylinder on said front-wheel side to the other (86; 234) of the two fluid chambers of said at least one fluid cylinder on said rear-wheel side; characterized by further comprising a diagnosing device (114, 116, 130, 140; 310, 320, 322, 324; 310, 372, 374) including a fluid-pressure detecting device (114, 116; 320, 322; 372, 374) operable to detect fluid pressures in said two fluid passage systems, said diagnosing device being operable to determine that said fluid circuit has an abnormality of fluid leakage, when a raised one of the fluid pressures in said two fluid passage systems detected by said fluid-pressure detecting device during turning of the vehicle causing an inclination of the body of the vehicle that causes said body to have a lower height on an outer side of a path of turning of the vehicle is lower than a lower limit determined by a force acting on said body so as to cause said inclination. a fluid circuit (76; 281; 380) including (a) at least one fluid cylinder (30, 60; 180; 210, 212, 226, 228) provided on each of a front-wheel side and a rear-wheel side of the vehicle, each of said at least one fluid cylinder including a housing (36, 66; 182; 230), and a piton (38, 68; 194; 236) which separates an interior space of the housing into two fluid chambers (80, 82, 84, 86; 232, 234), said each fluid cylinder being disposed between a wheel-side member (10, 12, 20, 50; 204, 206, 224) of the vehicle and a body-side member of the vehicle, such that there arises a difference between fluid pressures in said two fluid chambers when at least one of a left wheel (24, 54; 202, 222) and a right wheel (24, 54; 200, 220) is displaced in a vertical direction relative to a body of the vehicle, and (b) two fluid passage systems (72, 74; 250, 252; 350, 352) one (72; 250; 350) of which connects one (80; 232) of the two fluid chambers (80, 84; 232, 234) of said at least one fluid cylinder on said front-wheel side to a corresponding one (82; 232) of the two fluid chambers (82, 86; 232, 234) of said at least one fluid cylinder on said rear-wheel side, and the other (74; 252; 352) of which connects the other (84; 234) of the two fluid chambers of said at least one fluid cylinder on said front-wheel side to the other (86; 234) of the two fluid chambers of said at least one fluid cylinder on said rear-wheel side; characterized by further comprising a diagnosing device (114, 116, 130, 140; 310, 320, 322, 324; 310, 372, 374) including a fluid-pressure detecting device (114, 116; 320, 322; 372, 374) operable to detect fluid pressures in said two fluid passage systems, said diagnosing device being operable to determine that said fluid circuit has an abnormality of fluid leakage, when a raised one of the fluid pressures in said two fluid passage systems detected by said fluid-pressure detecting device during turning of the vehicle causing an inclination of the body of the vehicle that causes said body to have a lower height on an outer side of a path of turning of the vehicle is lower than a lower limit determined by a force acting on said body so as to cause said inclination.