  We consider quasiparticle charge and energy imbalances in a thin
superconductor weakly coupled with two normal-metal electrodes via tunnel
junctions at low temperatures. Charge and energy imbalances, which can be
created by injecting quasiparticles at one junction, induce excess tunneling
current $I_{\rm ex}$ at the other junction. We numerically obtain $I_{\rm ex}$
as a function of the bias voltage $V_{\rm det}$ across the detection junction.
We show that $I_{\rm ex}$ at the zero bias voltage is purely determined by the
charge imbalance, while the energy imbalance causes a nontrivial $V_{\rm
det}$-dependence of $I_{\rm ex}$. The obtained voltage-current characteristics
qualitatively agree with the experimental result by R. Yagi [Phys. Rev. B {\bf
73} (2006) 134507].
