  We calculate the scattering $T$-matrix of $I=0$ $\bar K N-\pi \Sigma$ coupled
channels taking a ladder sum of the Weinberg-Tomozawa interaction without
on-shell factorization, regularizing three types of divergent meson-baryon loop
functions by dimensional regularization and renormalizing them by introducing
counter terms. We show that not only infinite but also finite renormalization
is important in order for the renormalized physical scattering $T$-matrix to
have the form of the Weinberg-Tomozawa interaction. The results with and
without on-shell factorization are compared. The difference of the scattering
$T$-matrix is small near the renormalization point, close to the observed
$\Lambda$(1405). The difference, however, increases with the distance from the
renormalization point. The scattering $T$-matrix without on-shell factorization
has two poles in the complex center-of-mass energy plane as with on-shell
factorization, the real part of which is close to the observed $\Lambda$(1405).
While the difference is small with and without on-shell factorization in the
position of the first pole, closer to the observed $\Lambda$(1405), the
difference is considerably large in the position of the second pole: the
imaginary part of the center-of-mass energy of the second pole without on-shell
factorization is as large as or even larger than twice that with on-shell
factorization. Also, we discuss the origin of the contradiction about the
second pole between two approaches, the chiral unitary approach with on-shell
factorization and the phenomenological approach without on-shell factorization.
