The present invention provides a folder binding device including a binding device main body part in which insertion holes are formed into which binding legs are inserted, operating parts which are attached to the binding device main body part in such a manner as to rotate on rotating projections at end portions thereof as fulcrums, and sliding parts adapted to slide on the binding device main body part, wherein the sliding parts are connected to the operating parts via hinge parts in such a manner as to be activated by rotary operations of the operating parts to slide on the binding device main body part, whereby both fastening and unfastening operations of binding legs are made simple and a stable fastening of the binding legs is enabled.