A new measurement of the ratio of the branching fractions $R(D^{(*)}) = \mathcal{B}(\overline{B}\to D^{(*)}\tau^-\overline{\nu}_\tau) / \mathcal{B}(\overline{B}\to D^{(*)}\ell^-\overline{\nu}_\ell)$, $\ell = e, \mu$ is performed using a semileptonic tagging method with the data sample of $772 \times 10^6$ $B\overline{B}$ pairs collected at the Belle experiment. The obtained results are $R(D) = 0.307 \pm 0.037 \mathrm{(stat.)} \pm 0.016 \mathrm{(syst.)}$ and $R(D^*) = 0.283 \pm 0.018 \mathrm{(stat.)} \pm 0.014 \mathrm{(syst.)}$. These results are consistent with the SM prediction within $0.2\sigma$ and $1.1\sigma$, respectively. Belle also performs the polarization measurements in $\overline{B}\to D^{*}\tau^-\overline{\nu}_\tau$ decays. The first preliminary result of the fraction of the longitudinal polarization of $D^{*-}$, $F_L^{D^*}$, is obtained to be $F_L^{D^*} = 0.60 \pm 0.08 \mathrm{(stat.)} \pm 0.04 \mathrm{(syst.)}$ with an inclusive tagging method. The $\tau$ polarization measurement which has been performed earlier is also shown.