To prevent the generation of a premature start by guiding the regular start of respective boats by generating a sound only when the start of boats is discriminated to be regular and announcing it to competitors.

Laser beams emitted from laser emitting parts 4a, 4b and 4c arranged at prescribed intervals on an approach run water channel 30 in the front of a start line 50 are received by light receiving parts 5 installed on boats 10 and this method is composed of a stage for calculating the speed and acceleration of any relevant boat 10 from the time, when these laser beams are received, through an arithmetic part 6 installed on the boat 10, stage for predicting the start line passing time of the boat 10 based on this calculated result through the arithmetic part 6 and discriminating the regular start when it can be predicted that the position of the boat 10 at this predicted time is located inside a specified block 80 set in the front of the start line 50 with a fixed space inbetween, and stage for outputting a signal to a guide sound generating part 8 installed on the boat 10 and generating sound when the arithmetic part 6 discriminates the regular start.