In this paper, we address finite-time input-to-state stability (ISS) problem for switched nonlinear systems. We first show the relationship between finite-time ISS and the finite-time ISS-Lyapunov function for switched systems. Then we prove that a switched nonlinear system is finite-time ISS under average dwell-time switching signals if each constituent subsystem is finite-time ISS. Moreover, we analyze the optimal costs for a class of switched finite-time stabilizing systems and for their relaxed differential inclusions, respectively.