A detection device for a 3D printer and a 3D printer are provided. The detection device includes: a housing defining at least one feed port, a discharge port, a feed channel, and a discharge channel, the feed channel and the discharge channel form an internal cavity, and at least one hole in communication with the internal cavity is provided; at least one magnet respectively arranged in a hole, an end of the magnet inserted into the internal cavity is shaped with an end surface, such that when the printing filament is fed to a position of the magnet, the tip of the printing filament presses the end surface, thereby pushing the magnet to move to a predetermined position; and at least one Hall sensor, arranged to cooperate with a corresponding magnet, such that the Hall sensor is triggered when the corresponding magnet moves to the predetermined position.