The purpose of this study was to investigate the validity of the simple swimming power estimationmethod using Drag Boat. Drag Boat is as large as a floating kickboard. The body is made of wood, andthe load can be selected from five different levels. Drag force and swimming power can be calculated bymeasuring swimming velocity.The subjects were 22 male competitive swimmers. They swam 25m front crawl at maximum effort.This swimming speed was defined as Maximal Swimming Velocity (MSV). Thereafter, subjects swam 15mtow swimming with 5 different loads.The maximal swimming power (MSP) calculated with 5 different loads was 113.87 ± 25.91 W, andthe MSP calculated with 3 different loads was 113.94 ± 26.49 W. As a result of comparing the MSPcalculated by the two methods, there was no statistically significant difference. The above results showthat method of calculating with 3different loads is effective.