  We consider the flux jump instability of the Bean's critical state arising in
the flux creep regime in type-II superconductors. We find the flux jump field,
$B_j$, that determines the superconducting state stability criterion. We
calculate the dependence of $B_j$ on the external magnetic field ramp rate,
$\dot B_e$. We demonstrate that under the conditions typical for most of the
magnetization experiments the slope of the current-voltage curve in the flux
creep regime determines the stability of the Bean's critical state, {\it i.e.},
the value of $B_j$. We show that a flux jump can be preceded by the
magneto-thermal oscillations and find the frequency of these oscillations as a
function of $\dot B_e$.
