In an aligning mechanism of a 3D printer scanning device, a scan driving module includes a base and a motor, and the motor has a driving gear. The scan loading module includes a loading table, a turntable, and an engaging gear connected to the turntable, and the loading table has a notch, and the engaging gear is exposed from the notch. The driving gear of the scan driving module and the engaging gear of the scan loading module have a rounded corner or a positioning portion, so that the driving gear is engaged precisely with the engaging gear.