Starting from the continuity equation of the guiding center distribution function, we have obtained the kinetic equation which describes the field-aligned particle flux distribution per unit magnetic intensity, V∥ f/B, for adiabatic processes in a magnetized plasma under the constraint of the magnetic moment conservation. In additional to the along a particle dynamical orbit, the derived equation contains a term due to the convergence or divergence drift motions which depend on a sign of charges. In the bounce-average configuration, effects of this additional term on the localized accumulation of the trapped particle population are examined in association with the stationary, large-scale convection in the magnetosphere. It is shown that the main contribution to the local charge accumulation in the field-aligned current region comes from the curvature drift motion due to the perturbed magnetic field relating to the field-aligned current. Another utilization of the kinetic equation is demonstrated in obtaining an expression of the differential energy spectrum of precipitating particles from a magnetically trapped region.