Dependence of RF permeability (??RF = ??'RF - j ??''RF) on a bias magnetic field (H: corresponding to a signal field) in a permalloy film, when H and RF exciting magnetic fields (HRF) are in the direction of the hard axis in Permalloy films, was analyzed with the film taken as a single domain, the demagnetizing field in the film plane taken as 0, HRF assumed to be sufficiently small compared with the anisotropic field HK, and H assumed to be static. It was found that the ??'RF change is sharp at ?? ≪ ??K (????: ferromagnetic resonance frequency at H = 0) and the ??''RF change is sharp at ?? ?? ??K.