We evaluate the measurement accuracy of the branching ratio of $h to tau ^+ tau ^-$ at $sqrt{s} = 250$ GeV and 500 GeV at the ILC with the ILD detector simulation. For the $sqrt{s} = 250$ GeV, we assume the Higgs mass of $M_h = 120$ GeV, branching ratio of $mathrm{Br}(h to tau ^+ tau ^-) = 8.0 %$, beam polarization of $P(e^-, e^+) = (-0.8, +0.3)$, and integrated luminosity of $int L dt = 250 mathrm{fb ^{-1}}$. The Higgs-strahlung process $e^+ e^- to Zh$ with $Z to e^+ e^-$, $Z to mu ^+ mu ^-$, $Z to qbar{q}$ mode are analyzed. The measurement accuracy is calculated to be $Delta (sigma cdot mathrm{Br}) / (sigma cdot mathrm{Br}) = 3.5 %$. The scaled result to $M_h = 125$ GeV is estimated to be $4.2 %$. For the $sqrt{s} = 500$ GeV, we assume the Higgs mass of $M_h = 125$ GeV, branching ratio of $mathrm{Br}(h to tau ^+ tau ^-) = 6.32 %$, beam polarization of $P(e^-, e^+) = (-0.8, +0.3)$, and integrated luminosity of $int L dt = 500 mathrm{fb ^{-1}}$. The Higgs-strahlung process $e^+ e^- to Zh$ with $Z to qbar{q}$ mode and $WW$-fusion process $e^+ e^- to u_e bar{ u_e} h$ are analyzed. The measurement accuracy is calculated to be $Delta (sigma cdot mathrm{Br}) / (sigma cdot mathrm{Br}) = 5.7 %$ for Higgs-strahlung with $Z to qbar{q}$ and $7.5 %$ for $WW$-fusion.
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