PROBLEM TO BE SOLVED: To provide a sling tool length determination method in a training device which allows the length of a sling tool to be properly determined.SOLUTION: The sling tool length determination method determines the length of a sling tool in a training device which has the sling tool to hang a user U1 so as to provide balance training in which a moving body 9 performs a specific movement in a state where the user U1 is on the moving body 9 and the user U1 operates traveling of the moving body 9 by shifting his/her weight in accordance with the specific movement of the moving body 9. The length L of the sling tool is determined so as to satisfy a formula represented by Lmin
