at this time the amplification means 12 a 12 b in fig6 perform the processing corresponding to the gain regulators vca 3 a 3 b shown in fig4 the subtracting amplification means 13 in fig6 performs the processing corresponding to the subtracting amplifier 4 shown in fig4 the summing amplification means 14 in fig6 performs the processing corresponding to the summing amplifier 5 shown in fig4 and the amplification factor setting means 15 in fig6 performs the processing corresponding to the integrating circuit 6 a and reference voltage 6 b shown in fig4 accordingly in a similar manner as the previously described second embodiment shown in fig4 the feedback control of gain u03b2 of the amplification means 12 a 12 b is effected so that the output signal of the amplification means 12 b sum of vha vhb multiplied by gain is made constant by the output signal of the amplification factor setting means 15 the regulation is thereby possible so as to normalize the output signal position signal u03b4v of the amplification means 12 a accordingly it is possible in a similar manner as the first to third embodiments to readily perform the correction processing and to thereby effect the position detection at high accuracy without operation for obtaining parameters to correct error due to variance of individual magnet or temperature of hall effect device and without operation for making a correction according to each individual apparatus further since a feedback route from the amplification factor setting means 15 to the amplification means 12 a 12 b is made smaller so as to make an operation size smaller a settling time of the position detecting circuit can be made shorter.