As magnetic material has magnetic hysteresis characteristics, there is a problem that gives an error in current sensor output. So it is important to clarify the influence of magnetic hysteresis phenomena in current sensor. The object of this paper is to propose a method in consideration of a magnetic hysteresis in a FEM software JMAG, and to analyze the current sensor using the proposed method. Magnetic loops are approximated by a sigmoid function. We propose a method for coupling magnetic hysteresis and an external circuit to change the detecting current in response to gap magnetic flux density. And it clarifies the error in current sensor due to magnetic hysteresis.