The Mizushima Rinkai Railway was founded in 1970 as a JNR subsidiary to take over operations of the Mizushima Line and it’s branches from the Kurashiki Transportation Bureau.
The 11,2Km-long Mizushima Line was opened in 1943, during the war, as a link between the San’yo Main Line and Mitsubishi’s Mizushima Aircraft factory, wich was vital for the war effort.
After the war, in 1947, the Mizushima Line was transferred to the Kurashiki municipal government as a means for industrial development in the area, and one year later, passenger services operated by the Kurashiki City Transportation Bureau began on Kurashiki-Mizushima section of the line. In 1962 the new 3,6Km-long Koto and the 800m-long Nishi-Futo freight-only lines were opened, serving the eastern and western sides of the docks respectively.
By the late 1960s, the Mizushima Line was in dire need of a modernization, but as the Kurashiki municipal government did not have enough funds, the line was transferred to the newly-formed Mizushima Rinkai Railway on the 1st of April 1970. The line was converted to CTC signalling in 1971, in 1972 passenger services were extended to Mitsubishijiko-mae and in 1992 the section between Mitsubishijiko-mae and Urata stations was elevated.
As of today, the Mizushima Rinkai Railway operates both freight and passener services, run with a variety of diesel railcars (including some rare ex-JNR serieses for wich the line is famous) with the Mizushima Main Line now acting as Mizushima and Kurashiki cities’ very own urban railway.
Between the closure of the Dowa Mining Railway Katakami Line in 1991 and the opening of the Chizu Express Railway in 1994, the Mizushima Rinkai Railway was the only non-JR railway line operating passenger services on a non-electrified line in Okayama prefecture.