A superconducting magnet for a Fixed Field Alternating Gradient (FFAG) accelerator has been proposed. The required magnetic field is static and proportional to the k-th power of the orbit radius where k is the geometrical field index of the accelerator. In 2D, the required magnetic field can be generated with the optimized cross section of the coil. The cross section of the coil is a left-right asymmetry to simplify the cross section and ellipse to downsize the magnet. Local and integral 3D fields along the beam trajectory are evaluated with using new type of 3D coil configuration.