New interpretation of virtual time is proposed. This paper focuses on virtual time, a scalarparameter considered in time scale transformation, and its behavior. Both of them are analyzed as poten-tial of a state space. A theorem of the existence of virtual time is shown with Poincare lemma, and Liederivative yields a reciprocal of a time scaling function in autonomous systems. Geometric analysis derivesa similarity measurement of two virtual time. Moreover, once virtual time is given, regions where time scaletransformation can be applied are graphically determined as subspaces of a state space.