  The $O(a)$ improved Wilson quark action on the anisotropic lattice is
investigated. We carry out numerical simulations in the quenched approximation
at three values of lattice spacing ($a_{\sigma}^{-1}=1$--2 GeV) with the
anisotropy $\xi=a_{\sigma}/a_{\tau}=4$, where $a_{\sigma}$ and $a_{\tau}$ are
the spatial and the temporal lattice spacings, respectively. Using the
dispersion relation of mesons, the bare anisotropy $\gamma_F$ in the quark
action is numerically tuned below the charm quark mass region with the
statistical accuracy of 1 % level. The systematic uncertainties in the
calibration are examined and found to be under control in the continuum limit.
Then we compute the light hadron masses and find that they are consistent with
the result of the UKQCD Collaboration on the isotropic lattice. The effect of
the uncertainty in the calibration on the hadron spectrum for physical quark
masses is also found to be under control.
