An image formation apparatus is provided that prevents a belt from becoming displaced or detached from a belt unit. When a belt unit is detached from a main body casing, a tension roller is fixed in an outwardly protruding position by a fixing member. Thereby, the conveyor belt is stretched such that the conveyor belt is configured to be prevented from becoming displaced or detached. When the belt unit is mounted in the main body casing, fixation of the tension roller by the fixing member is released by a releasing protrusion and a suitable operating tensile force is imparted to the conveyor belt by coiled springs provided on the main body casing side.