Though the human standing posture is disturbed constantly by various external and internal factors, antigravity muscles and their antagonists, etc. work at every moments to prevent from falling but causing minute sway, in which control mechanism of posture holding would be hidden. It was verified the postural sways in each of lateral and antero-posterior axes respectively show normal Gaussian stochastic processes. In addition, the amount of the sway at an arbitrary time would be related more or less to those in the past, the postural sway, therefore, can be considered as an autoressive process.
Autoregressive power spectra of postural sways in the both axes showed a considerable nonperiodic power around 0Hz and less prominent periodic ones around 4Hz and 8-9Hz respectively. The periodic sways in the antero-posterior axis were more eminent than those in the lateral axis.
