Abstract: A 3D printer including two tanks, a powder spreading mechanism and a transport assembly is provided. A tank opening is defined on each tank, and an elevating mechanism is arranged in each tank. The powder spreading mechanism is able to move across the tank openings, one of the tanks contains powders for supplying the powders, and the powder spreading mechanism push the powders into the other tank. The transport assembly includes a carrying plate and a covering case, the carrying plate is arranged on the elevating mechanism in the tank for powder supplying, multiple insertion holes are defined at the carrying plate, a case opening is defined at the covering case, the covering case covers on the corresponding tank opening, multiple movable latches for correspondingly inserted in the respective insertion holes are arranged at the case opening, and the powders are allowed to be contained in the covering case.