The first 50000 series set, 51001, was delivered in November 2004 and entered service on the Tobu Tojo Line on 16 March 2005, followed by second-batch set 51002 in October 2005. The second set differs in having an emergency door in the front ends, and externally resembles the 50050 series used on the Tobu Skytree Line (see below).

Two more sets, 51003 and 51004, were delivered during fiscal 2009. 51003 was delivered to Shinrinkōen Depot in January 2010, followed by 51004 in February 2010. These two sets have pairs of opening windows and interiors based on sets 51061 onward.