With the intention of issuing an alert responsive to judgment of dozing at wheel or deviation from the lane, there is provided an alert system installed in a vehicle including driving state detecting device for detecting driving state of the vehicle; a mobile telephone including a camera; holding device for detachably holding the mobile telephone in an interior of the vehicle such that the camera is able to acquire an image ahead of the vehicle; and alert issuing device for issuing an alert from the mobile telephone based on the image ahead of the vehicle obtained by the camera and the driving state detected by the driving state detecting device.