To provide an article left behind alarm system of an automatic teller machine capable of quickly issuing an alarm when a portable object such as a bag, a trinket box and a wallet is left behind.

A mounting space part (20, 40 and 11D) where a portable object can be placed near an operation panel is provided with a portable object sensing means (21, 41 and 51), and a user sensing means (22) is provided in the automatic teller machine or near the automatic teller machine. The portable object sensing means senses that a user's portable object is put on the mounting space part, the user sensing means senses the existence of the user within a prescribed area in front of the automatic teller machine, a control means (24) issues an alarm signal and an alarming means (23) issues an alarm to the user when the user leaves the prescribed area in front of the automatic teller machine with the portable object put on the mounting space part.