  Study of the production and decay of scalar tau lepton ($\st$) at future
$\epem$ colliders helps to determine the value of $\tan\beta$ through the
measurement of the polarization of $\tau$ lepton that arises from $\st$ decay.
Key maps of the parameter space of MSSM are presented. (talk presented at the
fifth workshop on Japan Linear Collider(JLC) at Kawatabi, Feb 16-17.)
