A physical quantity measuring method includes: (a) generating a synchronized input signal from an input signal, wherein the synchronized input signal is synchronized with a reference clock; (b) measuring a total number (Nsum) that is the sum of pulses of the reference clock included in each of n units of the synchronized input signal; (c) generating 2n deviation signals based on a delay of the synchronized input signal with respect to the input signal; (d) generating a deviation integration signal by subtracting the total values of n rear-half deviation signals from the total values of n front-half deviation signals; (e) converting the deviation integration signal into a number of pulses of the reference clock; and (f) calculating the average number (Nrave) of pulses of the reference clock included in one unit of the input signal, based on the total number (Nsum), the number (dNsum), and the number n.