In 1965, construction of Line 1 and Line 3 began. The subway was inaugurated on 16 September 1972, when the 5.2 km long initial section of Line 1 opened between Kami-Ōoka and Isezakichōjamachi stations. On 4 September 1976, Line 1 was extended in both directions: 2.8 km and 2 stations to the southwest (from Kami-Ōoka to Kaminagaya), and 0.7 km and 1 station to the north (from Isezakichōjamachi to Kannai); the 2.8 km long initial section of Line 3 between Kannai and Yokohama also opened that same day and through services between Line 1 and Line 3 began.