To provide a split type CT and a current detection circuit which enable detection of current with limited errors, while facilitating application thereof for the existing electrical circuit and moreover, allows application thereof, even in a current detector which differentiably combines two split type current transformers.

There are arranged a current transformer and a circuit device connected to the secondary winding of the current transformer. The current transformer is provided with two iron cores and at least two windings made splittable and recombinable and the circuit device comprises a first circuit means for measuring the current of a primary conductor of the current transformer, a second circuit means adapted to put an AC signal from one of the two windings, a third circuit means which is connected to the remaining one of the two windings and an adjusting means for correcting the results of the measurement from the first circuit means by an output of the third circuit means. The frequency of the AC signal put thereinto from the second circuit means is separated far from the frequency of the current of the primary conductor to be measured by the first circuit means.