To reduce a measurement error based on the strength change of a reception signal and to reduce distance measurement time by obtaining distance from the ratio of the DC component of the multiplication signal of transmission and reception signals to that of the multiplication signal of a signal where the transmission signal has been subjected to specific phase shift and the reception signal.

The oscillation (transmission) signals of both oscillators 10 and 15 are multiplied by a mixer 14 and are inputted to a multiplier 3 and a phase shifter 2. Also, the multiplication signal of a receiver 19 is multiplied by the oscillation signal of the oscillator 15 by a mixer 20, which is inputted to the multipliers 3 and 4 via an LPF 21. The multiplier 3 multiplies an input (transmission) signal from an LPF 17 by a signal (the multiplication value of the reception signal of the receiver 19 and the oscillation signal of the oscillator 15) from the LPF 21 before inputting to an LPF 5. On the other hand, a multiplier 4 multiplies a (transmission) signal obtained by phase-shifting by a specific amount using the phase shifter 2 by a signal from the LPF 21 before outputting to an LPF 6. A divider 7 obtains the ratio of the DC components of the signal where the passage of the AC components is rejected by the LPFs 5 and 6. Distance is calculated based on the ratio.