A scanning device includes at least one motor, an input tray, a pickup roller, a separation roller module, an ultrasonic sensor, a scanning module, a path switcher and a controller. The pickup roller is connected with the at least one motor. The separation roller module is connected with the at least one motor. The ultrasonic sensor includes an ultrasonic emitter and an ultrasonic receiver. The ultrasonic sensor is used for sensing that a single paper or multiple papers are fed in. The scanning module is used for scanning a plurality of papers. The path switcher is connected with the at least one motor. The at least one motor is capable of driving the path switcher to be switched to a first position and a second position. The controller is connected with the at least one motor and the ultrasonic sensor.