An image forming apparatus includes a main CPU, and, in an unused period in which the image forming apparatus is not used, the main CPU detects whether or not a person exists within a human detection range, on the basis of an output of a human detection sensor. When a person has been detected, by outputting a notification voice regarding an intruder, which indicates that the intruder has been detected, from a speaker, the main CPU notifies the surroundings of the image forming apparatus and also transmits an electronic mail including a message indicating that the intruder has been detected to an address that has been registered in advance and thereby notifies a user of a terminal of the address of the detection of the intruder.