A unidirectional clutch device has a driving board, multiple permanent magnets, and multiple clutching elements. The driving board has an axle hole and multiple holding recesses. The holding recesses are defined in the driving board and are arranged around and communicate with the axle hole. Each holding recess has a long end having a radial width and a narrow end having a radial width smaller than that of the long end. The permanent magnets are mounted on the driving board and are located at positions adjacent to the narrow ends of the holding recesses. The clutching elements are rotatably mounted respectively in the holding recesses and are made of a magnetically conductive material. Each clutching element is moveable in a corresponding one of the holding recesses toward the narrow end of the corresponding holding recess by an attraction of a corresponding one of the permanent magnets.