An input device includes a control portion for controlling the input device encrypts image data, which is data of an image displayed on a display surface of a display mechanism, and transmits it to the display mechanism, and a detection mechanism for detecting a position of the user's fingertip in an aerial-image display region encrypts position data, which is data of a detected position of the user's fingertip, and transmits it to the control portion. In addition, in this input device, at least a fraud against a position-data signal line which transmits the position data from the detection mechanism to a control board and a fraud against the control board can be detected by a fraud detection mechanism for detecting that a fraud against the input device.