  We introduce an asymptotic formula for calculating quantum mechanical and
quantum theoretical models with caustics, like the Nambu--Jona-Lasinio(NJL)
model. This asymptotic formula is given by the form attached the extra term,
which suppresses the divergence induced because of caustics, to the leading
term of the WKB approximation. This formula guarantees validity of the mean
field approximation of models with caustics.
