Patent ID: 8854704

Claim:
An image reading apparatus, comprising: a light source unit for irradiating light to a document; an image sensor for receiving reflected light from the document irradiated with light by the light source unit and outputting a first analog signal representing the intensity of the reflected light by a voltage; an attenuator including an input portion to which the first analog signal is input, a first resistor, one end of which is connected to the input portion and a second resistor, one end of which is connected to the other end of the first resistor and the other end of which is grounded and configured to generate a second analog signal by voltage-dividing the first analog signal at a predetermined voltage-dividing ratio by the first and second resistors; an analog processor for generating a third analog signal by amplifying the second analog signal with a predetermined gain; and an A/D converter for converting the third analog signal into a digital signal; wherein the voltage-dividing ratio is not higher than a ratio of a maximum value of the amplitude of an analog signal inputtable to the analog processor to a maximum value of the amplitude of an analog signal having a possibility of being output from the image sensor.