An easy-type unidirectional locking device is primarily composed of a base and a lid, and is interiorly provided with a roller and an axle base which is provided at two sides with respective barriers, being controlled by a control knob installed outside of the lid. The axle base is resilience-retrievable via a spring connected with the control knob. A rope enters the entrance on the bottom of the locking device, passes by one barrier at one side of the axle base, goes around the roller, and then passes by the other barrier, and finally goes out of the exit. When the rope is drawn clockwise, the barriers at the axle base will clamp the rope, thereby accomplishing a unidirectional locking device.