E233系2000番台は常磐緩行線と千代田線の直通用に設計された、E233系の地下鉄対応車です。幅の狭い車体と前面貫通扉が特徴で、中央線などに投入された幅広車体のE233系とは外観が異なります。
JR East Series E233-2000 was designed for through services between the Joban local tracks and the Chiyoda Line. Its narrow body and front gangway door distinguish this subway-compatible variant from the wider-bodied E233 trains introduced on routes such as the Chuo Line.