A position detecting device for detecting a position of a magnet configured to move over a first target point and a second target point in steps includes a first hall device configured to generate a first hall voltage, a second hall device configured to generate a second hall voltage, a subtractor configured to generate a subtraction voltage based on a difference between the first hall voltage and the second hall voltage, an adder configured to generate an addition voltage based on a combination of the first hall voltage and the second hall voltage, a divider configured to calculate a ratio of the subtraction voltage to the addition voltage, and a subtraction voltage changing unit configured to maintain the subtraction voltage at the first target point and the second target point and in a transition section between the first target point and the second target point to be constant.