An image formation device is provided with an endless belt wound around a driving roller and a driven roller, a driving helical gear integrally provided at an axial end of the driving roller and rotating integrally with the driving roller. The driving helical gear applies a rotational force and an axial force to the driving roller. A plurality of guiding ribs are provided to an inner surface of the endless belt, while a regulating portion is provided at least one of the driving roller and the driven roller. The regulating portion has a regulation surface. When the endless belt moves obliquely in a direction in which the driving helical gear applies the axial force to the driving roller, side surfaces of the guiding ribs contact the regulating surface and prevent the oblique movement of the endless belt.