To provide a folding device capable of suppressing occurrence of wrinkle and folding a sheet double.

This folding device is provided with a protruding part 143a_1 capable of advancing and retracting freely for a nip part formed by a pair of first rolls 143c composed of a pair of rolls bringing mutual peripheral faces into contact and protruding toward the nip part at a tip in the direction of advance, a blade member 143a in which the protruding part 143a_1 is butted on a paper arranged by letting a surface face the nip part when advancing toward the nip part, the protruding part 143a_1 enters the nip part by advancing furthermore, and a paper folded double is fed into the nip part, and a soft region 143c_2 which has lower hardness than that of other parts and makes a round in the peripheral direction of a peripheral face in a part for nipping the protruding part 143a-1 entering the nip part on respective peripheral faces of the pair of the first rolls 143c.