  We present here the solution for accretion disk structure, which describes
continuously the transition between optically thick and optically thin disk
regions. We show that the disk structure equations without advection, used
here, give two branches of solutions which do not intersect for
$L<L_{b}\lesssim 0.6 L_{\rm Edd}$ for $\alpha=1.0$ and $M_{BH}=10^8 M_\odot$.
For larger luminosities there are no global solutions of the equations without
advection. We suggest, as one of the possibilities, that advection becomes
important even before, at luminosities $\sim0.1L_{\rm Edd}$, when the inner
disk regions become unstable due to radiation pressure dominance and induce the
transition from optically thick to optically thin disk in the global solution.
