Disclosed is a headrest position adjusting device provided with a distance measuring device and drive motor units. The distance measuring device is provided with a plurality of detection electrodes and a detection circuit including a plurality of capacitance detection circuits and a computation circuit. The computation circuit uses capacitance values, position information from the detection electrodes, and a high-degree function with a degree of at least 3 to compute a high-degree curve in a two-dimensional coordinate system with capacitance on the y-axis and detection-electrode position on the x-axis. The computation circuit computes the highest-degree coefficient of the high-degree curve and determines the distance between a head and a front part of a headrest on the basis of the computed highest-degree coefficient. On the basis of the measurement result, the headrest position adjusting device moves the front part of the headrest towards the front or back of a vehicle.