A scanning apparatus having dual power mode is described. The scanning apparatus includes a detection module, a switch unit, and a power controller. The detection module detects a first voltage signal and a second voltage signal for generating a detecting signal. The switch unit receives the commands from the power controller for outputting the first voltage signal and/or the second voltage signal to the image acquiring device of the scanning apparatus. The power controller determines whether the first voltage signal is detected according to the detecting signal. While the first voltage signal is detected, the power controller controls the switch unit to output the first voltage signal and/or the second voltage signal to the image acquiring device. While the first voltage signal is not exist, the power controller controls the switch unit to output the second voltage signal to the image acquiring device.