  Recently Murayama and Nomura proposed a simple scheme to construct the gauge
mediation models, using metastable supersymmetry breaking vacua. It has a
possibility to predict the ultra light gravitino mass m_{3/2} \lesssim 16 eV,
while such a light gravitino may destabilize the metastable vacua. We
investigate stability of the metastable vacuum of their model. The transition
rate from the false vacuum to true ones is evaluated by numerical calculation,
including the Coleman-Weinberg potential destabilizing the metastable vacuum.
It is found that when the messenger sector is minimal, stability of the
metastable vacuum imposes an upperbound on squark mass M_{\tilde q} for the
ultra light gravitino as M_{\tilde q} \lesssim 1800 GeV at most. Squarks with
this mass may be found in the LHC experiments.
