The pianists usually spend much time for practicing the fingering skills as the purpose for wonderful music, but did ignore the occupation incident injury from lots of practice. To concern all researches of musician's injuries, most are to find out hurt part by survey. There is only few touch on ”correct posture” to avoid, however what is ”correct posture”? What kind of hurt will cause through lots of practice? This chapter will describes these issues: shoulder, elbow, wrist joints, and hand gestures four parts, and also did survey about the correct playing posture in upper extremities, and also analyzes every kind of Musician's injuries and reasons caused by playing piano. Through this study, the author hopes to reduce musician's injuries, and also provide the reference for piano begining players and piano teachers.