A phase difference detection device for detecting a phase difference between a reference signal (Ss or Sc) and a detection signal (So (Sd)) in accordance with a rotation position (Θ) of a measured object comprising: a reference counter for performing a count in synchronization with a predetermined first clock pulse and reset when a phase of the reference signal becomes a predetermined reference phase; a velocity detection unit for acquiring velocity information capable of specifying a rotation velocity of the measured object, wherein the velocity detection unit is configured for counting the number of pulses of the first clock pulse corresponding to an amount of fluctuation (ΔT), with respect to a first time length (Ts) corresponding to a predetermined reference phase range of the reference signal, of a second time length (Td) corresponding to the reference phase range of the detection signal; characterized in that the phase difference detection device further comprises: a pulse conversion unit for outputting a second clock pulse by using a time specified based on the velocity information and required for rotation of the measured object by an angle corresponding to one count of the reference counter as a pulse interval (Tp), wherein the pulse conversion unit is configured for outputting the second clock pulse by using, as the pulse interval (Tp), a value specified based on the number of pulses of the first clock pulse corresponding to the amount of fluctuation counted by the velocity detection unit and obtained by dividing the second time length (Td) by the number of pulses of the first clock pulse corresponding to the amount of fluctuation; and a phase count unit configured to be able to latch the count value counted by the reference counter every time a phase of the detection signal becomes the reference phase, count a number of pulses of the second clock pulse after the phase of the detection signal becomes the reference phase, and output a sum and/or a difference of the latched count value and the counted number of pulses. a reference counter for performing a count in synchronization with a predetermined first clock pulse and reset when a phase of the reference signal becomes a predetermined reference phase; a velocity detection unit for acquiring velocity information capable of specifying a rotation velocity of the measured object, wherein the velocity detection unit is configured for counting the number of pulses of the first clock pulse corresponding to an amount of fluctuation (ΔT), with respect to a first time length (Ts) corresponding to a predetermined reference phase range of the reference signal, of a second time length (Td) corresponding to the reference phase range of the detection signal; characterized in that the phase difference detection device further comprises: a pulse conversion unit for outputting a second clock pulse by using a time specified based on the velocity information and required for rotation of the measured object by an angle corresponding to one count of the reference counter as a pulse interval (Tp), wherein the pulse conversion unit is configured for outputting the second clock pulse by using, as the pulse interval (Tp), a value specified based on the number of pulses of the first clock pulse corresponding to the amount of fluctuation counted by the velocity detection unit and obtained by dividing the second time length (Td) by the number of pulses of the first clock pulse corresponding to the amount of fluctuation; and a phase count unit configured to be able to latch the count value counted by the reference counter every time a phase of the detection signal becomes the reference phase, count a number of pulses of the second clock pulse after the phase of the detection signal becomes the reference phase, and output a sum and/or a difference of the latched count value and the counted number of pulses. a pulse conversion unit for outputting a second clock pulse by using a time specified based on the velocity information and required for rotation of the measured object by an angle corresponding to one count of the reference counter as a pulse interval (Tp), wherein the pulse conversion unit is configured for outputting the second clock pulse by using, as the pulse interval (Tp), a value specified based on the number of pulses of the first clock pulse corresponding to the amount of fluctuation counted by the velocity detection unit and obtained by dividing the second time length (Td) by the number of pulses of the first clock pulse corresponding to the amount of fluctuation; and a phase count unit configured to be able to latch the count value counted by the reference counter every time a phase of the detection signal becomes the reference phase, count a number of pulses of the second clock pulse after the phase of the detection signal becomes the reference phase, and output a sum and/or a difference of the latched count value and the counted number of pulses.