automatic ticket gate; automatic turnstile
Refers to the automated gates at train stations that read IC cards or tickets.
Please touch your IC card to the automatic ticket gate.
自動改札 is the everyday shortened form, while 自動改札機 is the fuller, more formal/technical name for the same automatic ticket gate.
Compound of 自動 (automatic), 改札 (ticket inspection), and 機 (machine).