A paper inverting device includes a first sensor, a second sensor, a guiding structure, a power mechanism, and a controller. The power mechanism is used for driving rotation of the guiding structure. The first sensor is used for detecting the position of the paper. The second sensor is used for detecting the thickness of the paper. According to the sensing signals from the first sensor and the second sensor, the controller may determine the timing of rotating the guiding structure and the rotating direction and the rotating angle of the guiding structure. Consequently, the guiding structure may be controlled to stop the paper and further invert the paper.