1. A projection type image display device provided with an unauthorized use preventing system comprising: a controller to operate said projection type image display device; a condition memory to store information indicating a plurality of use conditions in an authorized use of said projection type image display device; a password memory to store a password for releasing a restriction on the use of said projection type image display device; a detector to detect a use condition of said projection type image display device at a power-on timing; and a processor to impose restrictions on normal operations which can be carried out with said controller for operating said projection type image display device, other than either power-off of the display device or a password verification operation, when the use condition detected by said detector does not match at least one use condition indicated by the information stored in the condition memory; wherein, during the restrictions imposed by said processor said normal operations which can be carried out with said controller, other than power-off or the password verification operation, 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, wherein the plurality of use conditions include an “Orientation of Device”, a “Condition of Input to Input Terminal” and a “Fixing Condition of Device” condition.