1. An operation input device, comprising: a display; a camera capturing an image of an operator; a hand/finger image detector acquiring a frame image captured by the camera, and detecting a hand/finger image presenting a hand or finger of the operator from the frame image; an operation region specifier specifying an operation region in which the operator's operation is effective from a field of view of the camera based on the position or size in the frame image of the hand/finger image detected by the hand/finger image detector; a region map maker mapping the operation region specified by the operation region specifier on a display region of the display, and creating mapping information presenting the correspondence of coordinates between the operation region and the display region; and an operation input signal creator converting the coordinates in the operation region of the hand/finger image detected by the hand/finger image detector to the coordinates in the display region using the mapping information, and creating an operation input signal presenting the operator's operation input based on the position or size or shape of the hand/finger image at the converted coordinates.