An alert system includes a display device, a display control unit, and a target recognition unit. The display control unit: when the number of targets recognized by the target recognition unit is equal to or more than an upper limit number, sets a display range of a surrounding icon as a whole circular area; and in a state where the number of targets is equal to or more than the upper limit number and the display range of the surrounding icon is set as the whole circular area, when the number of targets increases, reduces the size of the surrounding icon.