Using motion capture system and floor reaction force gauge, we studied whether trunk posture relates to shoulder condition during piano playing or not. Eleven music college school students having ill or well-conditioned shoulders (four and seven volunteers, respectively) played two kinds of piano etude (scales and arpeggio), and we audited possible influencing factors. As the results, two factors associated with trunk spin are found. One is steady spin of part of trunk and the other is reverse spin of trunk toward shoulder spin. We recognized that the ill-condition group has lower reverence spin force against degree of spin at lower part than the other group, although sample numbers is very small.