To accurately measure the distance between a radio transmitter and a radio receiver being placed under multi-path environment by measuring the distance between the transmission and reception points of an electronic wave by a detected top path.

First, a top path is detected from a delay profile by a top path detection part 21 on a delay profile. The top path detection part 21 eliminates noise by averaging the delay profile in terms of time and then detecting a top path from each path that has been detected, signal for measuring distance is transmitted from a transmitter 10 at time t0. Time when a signal is received by a transmission/reception part 23 of a receiver 20 is set to t1, then distance L between transmission/reception points is given by L=C(t1-t0) since the propagation speed of an electronic wave is a light speed C. When the delay time difference between the top path obtained from a delay time difference measurement part 221 and the maximum level path is set to τ, an approximate value L' of the distance between the transmission/reception points is given by L'=C(t1'-τ-t0). Then, by correcting the approximate value of distance by a correction part 224, the approximation accuracy can be improved.