To provide an image reader in which the configuration is simplified by integrating an optical detection means and a dimmer means are formed on the same printed circuit board.

An original 2 placed on a contact glass 1 is emitted by a light source 5 and reflected image light from the original 2 is led by mirrors 6, 7, 8 provided to a 1st optical carriage 3 and a 2nd optical carriage 4, the image is formed on a CCD 10 via a lens 9 to read an image of the original 2. Through the constitution above, an inverter 11 lighting the light source 5, a photodetection section detecting the quantity of light emitted from the light source 5 and a dimmer section adjusting the luminous quantity are integrated on the same printed circuit board. Thus, related components are designed into a unit, the number of components is reduced, assembling man-hours are decreased and the reader is made small in size and light in weight.