To provide a method for measuring frequency in which the time resolution of frequency measurement is smaller than the frequency of inputted sine wave signal.

The method has a shaping step 30 for shaping an original signal into a sine wave signal and making its output an input signal y, a secondary differentiating step 10 for calculating a secondary differential y" of input signal y by the time, a division calculation step 11 for calculating the ratio of the secondary differential y" and the input signal y, an absolute value calculation step 12 for calculating the absolute value of the output of the division calculation step, and a square root extraction step 13 for calculating the square root of the output of the absolute value calculation step.