The trains were introduced in 1984, coinciding with the opening of the section of the Hokuso Line between Komuro and Chiba New Town Chūō.
The trains were initially classified as "2000 series", and formed as six-car sets.
The two six-car train sets were lengthened to eight cars each in 1991, coinciding with the start of inter-running services to and from the Toei Asakusa Line.
In 1994, the trains were reclassified 9000 series to avoid confusion with the Keikyu 2000 series trains on the Keikyu Main Line, over which the trains also inter-ran.
The trains were introduced in 1984, coinciding with the opening of the section of the Hokuso Line between Komuro and Chiba New Town Chūō. The trains were initially classified as "2000 series", and formed as six-car sets. The two six-car train sets were lengthened to eight cars each in 1991, coinciding with the start of inter-running services to and from the Toei Asakusa Line. In 1994, the trains were reclassified 9000 series to avoid confusion with the Keikyu 2000 series trains on the Keikyu Main Line, over which the trains also inter-ran.
Chiba New Town Railway 9000 series