This disclosure provides a phase measuring device that can measure phase differences with high precision using the digital circuits. A phase measuring device includes a buffer delay measuring circuit and a phase difference measuring circuit which use a TDC, respectively, and a phase difference calculator. The buffer delay measuring circuit generates delay measurement data indicating a delay amount τB between the buffers of the TDCs based on a highly precise clock signal and a sampling reference signal. The phase difference measuring circuit generates a number data row indicating a phase difference between measuring signals SS(A) and SS(B), and first and second phase difference measuring data Ds(A) and Ds(B), using the clock signal. The phase difference calculator calculates the phase difference using numbers of state data NB(A) and NB(B) based on the first and second phase difference measuring data Ds(A) and Ds(B), the number data row, and the highly precise delay amount τB obtained from the delay measurement data.