Relation between the internal magnetic field B_int and the angle θ is drawn according to Eq. (22). We set θ = θ_m which means the magnetic axis of the neutron star is aligned in the direction of the dipole axis. The black horizontal lines represent the maximum value of the internal magnetic field limited by Eq. (2). We show two conditions, which are B_int = 10^14.5 G and B_int = 10^13.5 G. Also, the green lines show the relationship between B_int and θ drawn from Eq. (22). Two different conditions are shown, B_int ∼ 10 B_dip and B_int ∼ B_dip. The colored areas show the allowable region.