To provide the image input device that decreases a position gap between a lens and a line sensor caused at assembling with an adjustment mechanism.

A line sensor 6 is placed at a rear part of a 1st lens with a low resolution initially, a read position by a focus and a line sensor is adjusted at this point of time, a focus of a 2nd lens 2 with other high resolution is adjusted, a setting command for resolution changeover is sent and an operation instruction is given to a drive section 4 to drive the line sensor 6 which is moved by receiving this setting command. Then the drive section 4 is operated and the line sensor 6 carries a sensor holder 31 through a ball screw 5 and stops the sensor holder 31 at a selected position on the rear optical axis of the 2nd lens 2 with high resolution. In the case that an optical axis of the line sensor 6 adjusted and fixed at this position is not aligned with the optical axis of the 2nd lens 2 with high resolution in a direction Z, the alignment is made by turning Z direction adjustment screws placed to the left and right so as to move the 2nd holder 21 vertically.