  We review a relativistic approach to the heavy quark physics in lattice QCD
by applying a relativistic $O(a)$ improvement to the massive Wilson quark
action on the lattice. After explaining how power corrections of $m_Q a$ can be
avoided and remaining uncertainties are reduced to be of order $(a\Lambda_{\rm
QCD})^2$, we demonstrate a determination of four improvement coefficients in
the action up to one-loop level in a mass dependent way. We also show a
perturbative determination of mass dependent renormalization factors and $O(a)$
improvement coefficients for the vector and axial vector currents. Some
preliminary results of numerical simulations are also presented.
