To make possible coping with overcurrent by using a thin secondary coil, by winding two secondary coil wires around a ring type iron core, with the number of turns corresponding to a specified maximum current ratio of a primary current and a secondary current.

Two secondary coil wires 1a, 1b which are thinner than the conventional coil wire are wound together around a ring type iron core with the number of turns corresponding to 1/2 the maximum current ratio of a primary current and a secondary current. Tap terminals 4a, 4b are arranged on both ends of one secondary coil wire 1a, and tap terminals 4b', 4c are arranged on both ends of the other secondary coil wire 1b. The tap terminals 4b, 4b' of the two secondary coil wires 1a, 1b are connected and make a series connecting state. Otherwise, the tap terminals 4a, 4b' of the two secondary coil wires 1a, 1b are connected and the tap terminals 4b, 4c are connected, so that a parallel connecting state is obtained. When this current transformer is used at the maximum current ratio, a series connecting state is selected. When it is used at the minimum current ratio, a parallel connecting state is selected.