A roll blind includes: a safety cord connected to and wound around a chain pulley adapted to rotate the winding rod, the safety cord having a separated lower end so that one side defines a lowering cord for pulling down the blind material and the other side defines a raising cord for rolling up the blind material; a bidirectional clutch unit adapted to raise/lower the blind material, the bidirectional clutch unit being positioned between the chain pulley and a driving shaft of the winding rod, the bidirectional clutch unit having bidirectional protrusions formed on an inner peripheral surface of the chain pulley at an identical interval in a circumferential direction so that, when the lowering or raising cord is pulled, the winding rod rotates together with the chain pulley, the bidirectional clutch unit having a number of rollers positioned between respective bidirectional protrusions.