The magnetic field generated around high-voltage transmission lines influences nearby buildings. Though the field strength is of the order of a few μ T, it causes the flickering effect on CRT for computers as well as televisions. Under these circumstances, it is necessary to reduce the magnetic field strength within the buildings. The transmission configuration with out-of-phase counter lines, the attenuation due to inverse square law and the installation of magnetic shielding walls are considered and discussed through measurement and numerical simulation to find the way for effective remedy.