The exciting current characteristic is suggested as a new method of evaluating the core characteristic. The phase shifting characteristic and the difference between a positive and negative waveform of a balanced half-wave type magnetic phase shifter are calculated by using the exciting current characteristics of cores employed in it. From these theoretical analyses, it can be determined that the difference of a positive and negative waveform is caused by a difference of exciting current characteristics of two cores used in it, and it becomes larger in proportion to larger control-circuit resistance. An experiment was performed using two pairs of cores, in which one pair of exciting currents are identical and the other pair differ. Theoretical results are in good agreement with the experimental results.