A projector can be easily attached by mounting a connecting unit to a socket for illumination in an ordinary home. Since the projector includes a communication unit configured to receive an electronic mail, the projector updates an image signal and adjusts a diffusion degree of modulated light by a light-diffusion adjusting unit on the basis of contents of the mail received by the communication unit. Therefore, when a user desires to inform family members who will return home that the user suddenly has to go out, if the user transmits in advance, to the projector, a mail including a message for a family member who returns home, the family member who returns home turns on an illumination switch at the entrance, whereby the projector can start up, perform an illuminating function, and clearly project and display the message.