Abstract: A current measuring method in which a magnetic sensor is a torodial core having a conductor for carrying a current to be measured passing through the hollow portion of the toroid. A coil on the core is excited with an AC voltage such that the positive and negative voltages induced in the coil are equal in amplitude when the conductor is not carrying current. Current in the conductor generates a change in magnetic flux which change is measured by detecting the algebraic sum of the amplitudes of the positive and negative voltages. Simultaneously, the amplifier output is applied to the input side of the AC voltage or a second coil disposed in the magnetic sensor so as to establish a magnetic equilibrium. Current measuring apparatus according to this invention include two types of apparatus composed of hardware to which the above-mentioned current measuring method is applied.