A continuous body folding device includes a conveying part having a moving surface that moves while suctioning and holding a first region of a continuous body, the conveying part conveying the continuous body in the longitudinal direction thereof; a first folding reference part in which a first endless belt, which moves in a first circulatory pathway along a first virtual plane including the moving surface, moves along a first reference segment adjacent to a virtual line of the continuous body in the same direction at the same speed as the moving surface; and first guiding members that are disposed along the first reference segment, contact a second region of the continuous body, and fold the continuous body along the virtual line and move the second region toward the first region so that the angle formed by the first and second regions becomes smaller as the continuous body is conveyed downstream.