An image reading apparatus includes a scanning unit disposed in a box-shaped casing for scanning a stationary original in a sub-scanning direction to read the original; a supporting unit for supporting one side of the scanning unit in a main scanning direction and guiding the one side of the scanning unit in the sub-scanning direction; a driving source for moving the scanning unit in the sub-scanning direction; a drive transmitting unit for transmitting a drive of the driving source to the scanning unit; and first and second reinforcing plates attached to the casing along the sub-scanning direction for reinforcing the casing. The first reinforcing plate forms a guide unit for supporting the other side of the scanning unit in the main scanning direction and guiding the scanning unit in the sub-scanning direction. The driving source and the drive transmitting unit are fixed to the second reinforcing unit.