  We present an addendum/erratum to the paper "Weyl Groups and Birational
Transformations among Minimal Models" written by the author and published in
1995, adding the analysis of the "88-th" deformation type of a smooth Fano
3-fold with $B_2 = 4$ denoted as $n^o\ 13$, which was missing from the original
classification table by Mori-Mukai and added later to the list of smooth Fano
3-folds with $B_2 \geq 2$, while correcting the mistake pointed out by Eric
Jovinelly (also noticed earlier by Kento Fujita). We also correct other typos
and miscalculations, clarifying some points of ambiguity. The original paper is
an attempt to generalize the result of Y. Manin associating some Weyl groups to
Del Pezzo surfaces to the one associating certain Weyl groups to Fano 3-folds.
