A new demagnetization correction method is explained in this article. Since a magnetization curve in an open magnetic circuit is considerably affected by the demagnetizing field which depends on the shape of the magnetic material, the demagnetization correction is significantly important to evaluate the magnetic properties of magnetic materials. In the new demagnetization correction method, a proper closed magnetic circuit curve is obtained in a way that a curve defined as a mathematical function is repeatedly modified in a computer feedback loop. In the method, the distribution of the demagnetizing field inside the magnetic material is taken into account by using the finite-element method in the computer calculation. Some calculation results about rare-earth permanent magnets are shown, and it is revealed that the new demagnetization correction method is able to reproduce the measured curves in the closed magnetic circuit with much higher accuracy than that of the classical demagnetization correction method.