An alerting device, which alerts a driver of a vehicle when the driver is looking at a display unit of a mobile terminal equipped with a camera, includes a gaze determination portion, an alert command portion, and a circumstance determination portion. The gaze determination portion determines whether the driver is looking at the display unit based on an image captured by the camera of the mobile terminal. When the circumstance determination portion determines that a current circumstance is not a gaze allowed circumstance and the gaze determination portion determines that the driver is looking at the display unit, the alert command portion outputs a command to alert the driver of the looking at the display unit. The circumstance determination portion determines that the current circumstance is the gaze allowed circumstance when the vehicle is halted at an intersection by a red traffic light.