The effects of non-axisymmetric magnetic field on characteristics of a direct energy converter (DEC) with an axisymmetric cusp configuration are studied. The axisymmetric Cusp DEC (Kobe Cusp) is installed at the end of the GAMMA 10 device, which breaks the axisymmetry of the DEC. It is clarified that the nonaxisymmetric magnetic field changes the Störmer potential at the stagnation and the equilibrium electric field by the order of the perturbation field to the equilibrium magnetic field.