The Nagano Electric Railway 2100 series (長野電鉄2100系) is a DC electric multiple unit (EMU) train type operated by the Nagano Electric Railway in Japan on Snow Monkey limited express services since 26 February 2011, replacing the remaining ageing 2000 series trains.

They underwent modifications for wanman ("one man") driver only operation at Tokyu Car's Yokohama factory before being moved to the Nagano Electric Railway in December 2010 for final repainting.

[3] The trains were initially finished in the same livery of white, red, grey, and black, which they carried in the JR days.

Car 1 has reclining/rotating seating, and also retains the original private compartment, seating four persons, branded as "Spa Saloon" (Spa猿～ん, Spa sarūn), a pun on the Japanese word for monkey.

[5] On 8 September 2012, set E2 was returned to service following general overhaul repainted into a new livery of red and white.