In 1992, 400 series Shinkansen train-cars were manufactured and the Yamagata Shinkansen line started operation between Fukushima Station (located in Fukushima Prefecture) and Yamagata Station of the Ou main line; In 1997, E3 series Shinkansen train-cars were manufactured and the Akita Shinkansen line started operation between Morioka Station and Akita Station on the Tazawako line and the Ou main line; in 1999, E3 series 1000 - 1999 Shinkansen train-cars were manufactured additionally and the section between Yamagata Station and Shinjo Station of the Ou main line started operation as an extension of the Yamagata Shinkansen.
1992年に新幹線400系電車を新造し、山形新幹線として奥羽本線の福島駅(福島県)-山形駅が、1997年に新幹線E3系電車を新造し、秋田新幹線として田沢湖線・奥羽本線の盛岡駅-秋田駅が、1999年に新幹線E3系電車1000番台を増備し、山形新幹線の延伸として奥羽本線の山形駅-新庄駅が、それぞれ順次営業運転を開始した。