Radiation at the fundamental and higher harmonic frequencies from power lines affects the environment of Earth's ionosphere and magnetosphere, because such radiation may lead to the enhanced electron precipitation into the ionosphere due to wave-particle interactions in the magnetosphere. In this paper we analyze theoretically the penetration of power line radiation, taking into account the presence of the anisotropic, homogeneous ionosphere. The electromagnetic field can be formulated by using the Fourier transform and field distribution obtained by proper deformation of the integral path with consideration of singularities. We calculate the field distribution as a function of altitude and distance from the source. From the numerical results, we can find several new findings: (1) the effect of the radiation from power line is limited in a relatively narrow region below the cutoff frequency of the guided mode in the Earth-ionosphere waveguide, while the region affected by the power line radiation becomes much wider if the guided modes exist, (2) the radiated fields are directed almost horizontally, and (3) the altitude distribution of electromagnetic fields changes at the ion gyrofrequency. Comparison with the observed data shows a good agreement with respect to the region affected by power line radiation.