A duplex scanner comprising a first scanning module, a second scanning module, a transmission mechanism, a power source and a control processing unit is provided. The first scanning module scans a front side of a to-be-scanned document and captures a front side image of the to-be-scanned document. The second scanning module scans a back side of the to-be-scanned document and captures a back side image of the to-be-scanned document. The transmission mechanism moves the to-be-scanned document relatively to the first scanning module and the second scanning module. The power source outputs at least a feedback signal while driving the transmission mechanism. The control processing unit receives a scan command and accordingly controls the power source to drive the transmission mechanism. The control processing unit receives the feedback signal and accordingly controls the first scanning module and the second scanning module to proceed duplex scan.
