Since 3D-printer makes something by piling up thin layers, it is estimated that every 3D printer-made products have anisotropy. Therefore, it is expected that bending stiffness of gear teeth become uneven, and it increase gear noise and vibrations. In this study, the authors made several test gears with 3D-printer. These test gears have different laminating angles. Then the authors were measured bending stiffness of each gear's tooth, and investigated the relations between the interface direction and the tooth bending stiffness. As a result of this investigation, the angle between laminating interface and tooth trace affects tooth bending stiffness. When this angle goes 0 degree, tooth bending stiffness becomes minimum. On the other hand, the angle becomes 90 degrees, the tooth bending stiffness goes maximum. In conclusion, to make a gear which has even and large stiffness, the gear should be laminated when its shaft hole is vertical to the 3D-printer's table.