The Marunouchi to Kōnomiya section was opened by the Nagoya Railway in 1928, the Ichinomiya to Kasamatsu section was opened by the Meigi Railway in 1935, and by 1935 the line was dual track as far as Kanō. Meanwhile, the Aichi Electric Railway opened the Jingu-mae to Arimatsu section in 1917 (Arimatsu Line), electrified at 600 V DC, and extended the line to Toyohashi in 1927 (becoming the Toyohashi Line). The Narumi to Yahagibashi section was double-tracked in 1924, and by 1935, the line was double-tracked from Horita to the Hirai Signal Box. The voltage on the line was increased to 1,500 V DC in 1925.