A vehicle-mounted alert system includes display devices equipped to a vehicle, a sight line detection device detecting driver's sight line, a surrounding monitoring device detecting a presence of an object near the vehicle and a direction of the object with respect to the vehicle, and an alert control device controlling the display devices to display an alert image for informing the driver of the presence of the object detected by the surrounding monitoring device. The alert control device controls the display device located in a direction of the sight line of the driver to display the alert image, and then, controls the display devices so that the alert image successively moves from the display device located in the direction of the sight line of the driver to the display device determined based on the direction of the object detected by the surrounding monitoring device.