A folding device for folding continuous paper, which is previously provided with fold lines at given intervals, along the fold lines in a zigzag pattern. The folding device comprises a feeding member of the continuous paper, a swinger fin that swings using its one end as a fulcrum like a pendulum in synchronization with the fold lines while feeding the continuous paper into its inside, and a table to be surmounted by the continuous paper that has been folded. The swinger fin includes a feed roller pair for feeding the continuous paper while sandwiching the paper therebetween, and at least a pair of guide plates facing each other with a given gap therebetween, in which the continuous paper is fed through the gap. One of the feed rollers constructing the feed roller pair and one of the guide plates, which are located on one side of the continuous paper, can be integrally opened or detached from the swinger fin.