  In this paper, we describe a numerical approach to evaluate Feynman loop
integrals. In this approach the key technique is a combination of a numerical
integration method and a numerical extrapolation method. Since the computation
is carried out in a fully numerical way, our approach is applicable to one-,
two- and multi-loop diagrams. Without any analytic treatment it can compute
diagrams with not only real masses but also complex masses for the internal
particles. As concrete examples we present numerical results of a scalar
one-loop box integral with complex masses and two-loop planar and non-planar
box integrals with masses. We discuss the quality of our numerical computation
by comparisons with other methods and also propose a self consistency check.
