PURPOSE: To provide an apparatus capable of efficiently folding short strip like cut sheet paper with constant width cut into a constant dimension along the fold line extending in the longitudinal direction thereof.

CONSTITUTION: During a period when cut sheet paper P is sent in its longitudial direction while the lateral positional shift thereof is prescribed, by a flat belt 15 arranged in a twisted state over the front and rear of the linear gauge edge 3a of the gauge plate 3 arranged along the upper surface of the cut sheet paper P, the part exposed from the gauge edge 3a of the cut sheet paper P is bent along the gauge edge 3a.