  We find the novel effect on the decay of a false vacuum in view of quantum
field theory, which is induced by a field coupling to the scalar field related
to a first-order phase transition. This effect of the environment can never be
included in the traditional method using the effective potential, and, in fact,
acts as dissipative and fluctuation effects on tunneling phenomena. We show
that the decay of the false vacuum is drastically either enhanced or
suppressed. It is also clarified what kind of interaction enhance or suppress
the tunneling probability.
