  Presilting and silting subcategories in extriangulated categories were
introduced by Adachi and Tsukamoto recently. In this paper, we prove that the
Gabriel-Zisman localization $\mathcal B/({\rm thick}\mathcal W)$ of an
extriangulated category $\mathcal B$ with respect to a presilting subcategory
$\mathcal W$ satisfying certain condition can be realized as a subfactor
category of $\mathcal B$. This generalizes the result by Iyama-Yang for silting
reduction on triangulated categories. Then we discuss the relation between
silting subcategories and tilting subcategories in extriangulated categories,
this gives us a kind of important examples of our results. In particular, for a
finite dimensional Gorenstein algebra, we get the relative version of the
description of the singularity category due to Happel and Chen-Zhang by this
reduction.
