An exerciser for the sake of training the abdominal muscle group, wherein the operator may rotate on his backbone for taking a twisting exercise for his upper and lower bodies in reverse (different) direction; and wherein the exerciser includes a rotating disc mechanism for the lower limb of the operator to stand thereon and swiveled under application of force, a rotating handlebar mechanism for the upper limb of the operator to hold thereon and swiveled under application of force, and a coupling mechanism for synchronically and reversely coupling the rotating disc mechanism and the rotating handlebar mechanism.