  The tidal disruption event by a supermassive black hole in Swift J1644+57 can
trigger limit-cycle oscillations between a supercritically accreting X-ray
bright state and a subcritically accreting X-ray dim state. Time evolution of
the debris gas around a black hole with mass $M=10^{6} {\MO}$ is studied by
performing axisymmetric, two-dimensional radiation hydrodynamic simulations. We
assumed the $\alpha$-prescription of viscosity, in which the viscous stress is
proportional to the total pressure. The mass supply rate from the outer
boundary is assumed to be ${\dot M}_{\rm supply}=100L_{\rm Edd}/c^2$, where
$L_{\rm Edd}$ is the Eddington luminosity, and $c$ is the light speed. Since
the mass accretion rate decreases inward by outflows driven by radiation
pressure, the state transition from a supercritically accreting slim disk state
to a subcritically accreting Shakura-Sunyaev disk starts from the inner disk
and propagates outward in a timescale of a day. The sudden drop of the X-ray
flux observed in Swift J1644+57 in August 2012 can be explained by this
transition. As long as ${\dot M}_{\rm supply}$ exceeds the threshold for the
existence of a radiation pressure dominant disk, accumulation of the accreting
gas in the subcritically accreting region triggers the transition from a gas
pressure dominant Shakura-Sunyaev disk to a slim disk. This transition takes
place at $t {\sim}~50/({\alpha}/0.1)$ days after the X-ray darkening. We expect
that if $\alpha > 0.01$, X-ray emission with luminosity $\gtrsim 10^{44}$ ${\rm
erg}{\cdot}{\rm s}^{-1}$ and jet ejection will revive in Swift J1644+57 in
2013--2014.
