1. A projection type image display device provided with an unauthorized use preventing system comprising: a button unit or a remote controller for operating said projection type image display device; a condition memory for storing information indicating at least one use condition in an authorized use of said projection type image display device; a password memory for storing a password for releasing a restriction on the use of said projection type image display device; a detector for detecting a use condition of said projection type image display device at a power on timing; and a processor for imposing restrictions on the use of said projection type image display device operating with said button unit or said remote controller, when the used condition detected by said detector does not match the at least one use condition indicated by the information stored in the condition memory; wherein, during the restriction on the use of said projection type image display device, the processor releases the restrictions on the use of said projection type image display device when a password which is the same as the password in the password memory is input.