A device includes a memory that stores a measurement-result of a first magnetization of a permanent-magnet corresponding to an external-magnetic field in an open-magnetic circuit; and a processor to divide the permanent-magnet into meshes, generate a function based on the measurement-result, the function indicating a second magnetization corresponding to the external-magnetic field in a closed-magnetic circuit, the function including a parameter having a value, calculate a diamagnetic-field corresponding to the external-magnetic field based on the second magnetization for each of the meshes, calculate a third magnetization of the permanent-magnet, calculate an average of the third magnetizations, calculate an error between the first magnetization and the calculated average, correct the value of the parameter, and repeat the calculation of the second magnetization, the diamagnetic-field, the third magnetizations, the average, and the error, and the correction of the value of the parameter until the error falls below a threshold.