Current sensor using Hall device is an instrument of detecting a current by Hall effect. The existing current sensor is ordinarily worked by concentrating electromagnetism produced around the conducting wire turned iron core. The tiny curren, however, could not be accurately detected by the instrument owing to influence of residual magnetism exisisting in iron core, and the result of detecting is also somewhat on the large side. kAccordingly, We fabricated a new type of instrument minimizing the influence of residual magnetism existing in iron core and detected the tiny DC current accurately by taking advantage of magnetic modulation. The range of measuring DC current is 0[mA]-100[mA] and the maxiumm Linerity tolleance by the result of detecting current, can be reduced less than 3 percent.