The physical quantity measuring apparatus includes a first function of generating voltage used for position-controlling a movable body, a second function of detecting a position of the movable body during a position detecting period, a third function of calculating a control amount necessary to keep the movable body at a predetermined position on the basis of a detection result by the second function, and causing the first function to generate a control voltage corresponding to the calculated control amount to keep the movable body at the predetermined position during a position controlling period, and a fourth function of setting the position detecting period and the position controlling period in a time-sharing manner so that the position detecting period and the position controlling period do not overlap with each other.