Abstract: An improved cut length adjusting apparatus in a folding machine of a rotary press is disclosed. The folding machine generally includes only a cutting drum having two knife blades disposed along its circumference nearly at equal angular intervals, and a folding drum rotating synchronously with but in the opposite direction to the cutting drum. The knife drum is formed of an outer cylinder and an inner cylinder which are mutually rotatable and which each have one knife blade respectively projecting therefrom. The improvements reside in that a helical gear adapted to mesh with another helical gear at the axial end of the folding drum is provided at the axial end of at least one of the outer and inner cylinders, and either one of the helical gear at the axial end of the outer or inner cylinders and the helical gear at the axial end of the folding drum is movable in the axial direction.