Ni2MnGa alloy with 10M martensite exhibits rearrangement of martensite variants (RMV) by magnetic field, but Ni2.14Mn0.92Ga0.94 with 2M martensite does not. In order to explain the difference, we measured uniaxial magnetocrystalline anisotropy constant K-u and the stress required for twinning plane movement tau(req) in these alloys. Concerning the former alloy, the maximum value of magnetic shear stress acting across twinning plane tau(mag), which is evaluated as vertical bar K-u vertical bar divided by twinning shear, becomes larger than tau(req). On the other hand, concerning the latter alloy, the maximum of tau(mag) is only one-tenth of tau(req) at any temperature examined. Obviously, the relation, tau(mag)>tau(req), is satisfied when RMV occurs by magnetic field and vice versa. In this martensite, the large twinning shear of 2M martensite is responsible for small tau(mag) and large tau(req).