Transient current behavior through a nanoscale system responding to a sudden voltage application was investigated, based on the Liouville equation of density matrix. It was found that the transient current behavior is characterized with the oscillation and relaxation processes. The oscillation originates from the time-dependent electron transitions between the electrode and nanoscale system, and the period depends on the Fermi energy and the bandwidth of electrodes. On the other hand, the relaxation occurs due to the energy dissipation into a number of electronic states in electrodes, thus, the relaxation time depends on the density of states in electrode and the electron transfer energy between the electrode and nanoscale system. Furthermore, we clarified that the strong electron-electron interaction decreases the relaxation time.

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