In a color picture tube apparatus, a deflection unit is provided around a color picture tube and a leakage magnetic is generated from the deflection unit. A metal cover made of aluminum, which covers an electrical power source is located in a space to which leakage magnetic field is reached and a first opposition magnetic field is generated from the metal cover due to the leakage magnetic field which produces an eddy current in the metal cover. A metal plate made of a conductive and non-magnetic material is so located between the deflection unit and the metal cover as to be substantially perpendicular to the metal cover. Thus, a second opposition magnetic field is so generated from the metal plate due to the leakage magnetic field as to substantially cancel the first opposition magnetic field.