To allow a very small time interval to be measured, to enhance resolution while keeping a frequency of a reference clock signal low, and to realize high measurement precision.

Clock signals CLK1, CLK2 having a frequency difference ΔT are generated by oscillators 10, 20, a pulse transmission circuit 50 outputs a transmission pulse SP in response to the clock signal CLK1, receives a reflected pulse in response to thereto by a pulse receiving circuit 60, and outputs a reception pulse RP. A phase comparator 30 compares a phase of the clock signal CLK1 with a phase of the clock signal CLK2 to output an in-phase signal P1, a phase comparator 40 compares a phase of the reception pulse RP with a phase of the clock signal CLK2 to output an in-phase signal P2, a counter circuit 50 counts the clock signal CLK1 from the output of the in-phase signal P1 upto the output of the in-phase signal P2, and a time difference τ between the transmission pulse SP and the reception pulse RP is measured based on a count value and the frequency difference ΔT between the clock signals CLK1, CLK2.