The present invention relates to an image scanning apparatus having a scanning module, a transmission belt, a speed-change gear module, and a driving device. The driving device drives the transmission belt by using the speed-change gear module so as to drive the scanning module positioned on the transmission belt to scan an image. The speed-change gear module provides various speed-change ratios so that the driving device may drive the transmission belt at different speeds under the same speed of the driving device. In the embodiment, the speed-change gear module has a switching platform for accommodating the speed-change gear module. The stepping motor serving as the driving device is connected with the speed-change gear module by the motor gear. The transmission belt is connected with the speed-change gear module by the belt wheel. When moving or rotating the switching platform to switch between the deceleration ratios, a first set of deceleration gear and a second set of deceleration gear selectively engages with a motor gear.