This is the case study that the race pattern of a 400-m sprint was improved by “Affirmation”. The affirmation is a method of accomplishing goal and used in the world for business, education and so on. The purpose of this study was to obtain practical wisdom when using the affirmation to sports. A male sprinter had been having the problem of the 400-m race pattern and tried to solve it by the affirmation. Then, while correcting the affirmation sheet each time the race was done, the problem was solved four months from beginning to use the affirmation. He could not realize the image of the race pattern in the first half of the practical process. But in the second half of the practical process, he changed the contents of affirmation sheet greatly, realized the target model of race pattern which is the moderate deceleration type one month later. Besides, he had read the short affirmation sheet every day during this practice process. From this process, it was suggested that it is difficult to make the high-quality affirmation sheet in a short period from using it for the first time, and that it is necessary to use the short sentence involved realistic and clear image for continuous implementation of affirmation.