  We apply Borel resummation method to the conventional perturbation series of
ground state energy in a metastable potential, $V(x)=x^2/2-gx^4/4$. We observe
numerically that the discontinuity of Borel transform reproduces the imaginary
part of energy eigenvalue, i.e., total decay width due to the quantum
tunneling. The agreement with the exact numerical value is remarkable in the
whole tunneling regime $0<g\lsim0.7$.
