A header has a middle section disposed on a main frame and at least two side sections disposed adjacent to the middle section, a cutterbar extending substantially across the width of the header, and at least one conveyor device which conveys crop cut by the cutterbar laterally in the direction of the middle section. The conveyor device has a central conveyor including an endlessly circulating, endless conveyor belt which is guided around two rollers disposed on two support elements extending in parallel to the conveyance direction and are each mounted on bearing points provided on the support elements. The support elements each have a guide recess and in which one of the rollers is displaceable so that the conveyor belt can be transferred from an operating position, in which the conveyor belt is tensioned, into a maintenance position, in which the conveyor belt sags, in sections, in the vertical direction.