An image reading apparatus is provided which includes a cold-cathode tube as a light source for illuminating a document sheet, an inverter for providing the light source with driving power. A connection cable is used for electrically connecting the light source to the inverter. The image reading apparatus also includes three kinds of rows of light receiving elements arranged in the primary scanning direction for detecting the light reflected on the document sheet. A lens array is provided for focusing the reflected light at the respective rows of light receiving elements. The light receiving elements are mounted on a printed circuit board. The light source, the inverter, the lens array and the printed circuit board are supported by a single case of the image reading apparatus.