  We derive the evolution equations of parton distribution functions
appropriate in different kinematic regions in a unified and simple way using
the resummation technique. They include the Gribov-Lipatov-Altarelli-Parisi
equation for large momentum transfer $Q$, the Balitskii-Fadin-Kuraev-Lipatov
equation for a small Bjorken variable $x$, and the
Ciafaloni-Catani-Fiorani-Marchesini equation which unifies the above two
equations. We propose a modified Balitskii-Fadin-Kuraev-Lipatov equation from
the view point of the resummation. This modified version possesses an intrinsic
$Q$ dependence and its predictions for the structure function $F_2(x,Q^2)$ are
consistent with the HERA data.
