The nature of the glass transition of supercooled liquids is still surrounded by controversy. The current status of theoretical understanding of the transition is much more like that before the Currie-Weiss theory for critical phenomena in a sense that the full-fledged mean field theory is still not at hand. This, however, does not mean that we suffer from (literally glass-like) stagnancy in the progress. Contrarily, we witness a revolutionary development of the mean-field description of the slow dynamics near the transition escorted by the bona fide thermodynamic transition at a finite temperature. In this review, we start with the introductory discourse of the phenomenology of the glass transition and outline the whole picture of the glass transition which the contemporary version of the mean-field theory envisions. Furthermore, we present the results of our recent numerical study for a randomly pinned liquid, which strongly support the mean-field scenario. This is the first time forever that the true glass state with thermodynamic singularity has been generated in silico.