  We study constraints to avoid deep unrealistic minima in the next-to-minimal
supersymmetric standard model. We analyze a scalar potential along directions
where all of and one of the three Higgs fields develop their vacuum expectation
values, and find unrealistic minima deeper than the electroweak symmetry
breaking (EWSB) vacuum. These unrealistic minima threaten the realization of
the successful EWSB and therefore should be avoided. Necessary conditions to
avoid these minima result in constraints of parameters. We show that a wide and
significant region of the parameter space, especially large \lambda, is ruled
out by our constraints.
