In order to examine the function of muscle for control of posture a frequency analysis was performed of surface EMGs taken from the arm (M. deltoideus) held at the shoulder level. The results indicate that: (a) Power spectra first with a dominant especially with respect to 45-55 Hz component changed significantly 2 components of 5-60 Hz and 65-75 Hz when a 5 min experiment were repeated 3 times, and (b) the ratios of increased power was remarkable in both bands of 10-15 Hz and 30-35 Hz with repeating trials. The control of posture was discussed from the standpoint of behavioral psychology.