To provide a system for automatically and constantly measuring run time display with high precision without manual intervention.

The proposed system is provided with a radio wave transmitter 2 mounted on a boat 1, at least two antennas 3-5 which are fixed/arranged by sandwiching the extension line of a start line and the extension line of a goal line to receive radio waves radiated from the radio wave transmitter 2 and a receiver 6 connected to the antennas. The receiver 6 is provided with a phase analysis means 7 for detecting the passing instances of the start line and the goal line of the boat 1 based on the comparison of the phases of reception signals in the two antennas sandwiching the start line and the two antennas sandwiching the goal line and for outputting a start line passage signal and a goal line passage signal, and a timer means 8 for measuring run time from a time when the boat 1 passes the start line to a time when it passes the goal line based on the start line passage signal and the goal line passage signal.