The algorithm developed by Kamide, Richmond and Matsushita (KRM) has been extensively used in estimating ionospheric electric fields, ionospheric currents, and field-aligned currents over the entire polar region from ground magnetic chain data with a time resolution of about 5 min. However, in the KRM and some other similar methods, geomagnetic field lines are assumed to be effectively radial, so that it is important to estimate errors resulting from such an assumption. In this paper, an iteration scheme is developed in which realistic curved geomagnetic field lines are employed. We have reestimated both the ionospheric and field-aligned currents and found that the correction to the ionospheric currents and the field-aligned currents obtained from the KRM scheme is 5-20% in the high-latitude (60¿-80¿) region and is 15-35% in the middle latitude (<60¿) region.