A fastening device (100, 110, 120), comprising: a base (200, 200a, 200b); a spool (300, 300a, 300b) disposed at the base (200, 200a, 200b) and a lace wound around the spool (300, 300a, 300b); a knob (500, 500a, 500b) disposed at the base (200, 200a, 200b); and an engaging unit (400, 400a, 400b) disposed at the base (200, 200a, 200b); wherein the fastening device (100, 110, 120) further comprising: the knob (500, 500a, 500b) comprising a spiral track (530, 530a, 530b); the engaging unit (400, 400a, 400b) comprising a guiding portion (430, 430a, 432b) coupled to the spiral track (530, 530a, 530b); and wherein the engaging unit (400, 400a, 400b) has a first position and a second position relative to the knob (500, 500a, 500b), the engaging unit (400, 400a, 400b) prohibits the spool (300, 300a, 300b) from rotating toward a releasing direction when the engaging unit (400, 400a, 400b) is at the first position, the engaging unit (400, 400a, 400b) allows the spool (300, 300a, 300b) to be rotated toward the releasing direction when the knob (500, 500a, 500b) is rotated toward the releasing direction and the guiding portion (430, 430a, 432b) moves relative to the spiral track (530, 530a, 530b) to allow the engaging unit (400, 400a, 400b) to switch to the second position, characterized in that, the fastening device (100, 110, 120) comprising: at least one retaining portion (410, 410a, 410b, 420, 420a, 420b, 430b); and the at least one retaining portion (410, 410a, 410b, 420, 420a, 420b, 430b) is coupled to the knob (500, 500a, 500b) or the base (200, 200a, 200b) to allow the engaging unit (400, 400a, 400b) to be remained at the first position or the second position. a base (200, 200a, 200b); a spool (300, 300a, 300b) disposed at the base (200, 200a, 200b) and a lace wound around the spool (300, 300a, 300b); a knob (500, 500a, 500b) disposed at the base (200, 200a, 200b); and an engaging unit (400, 400a, 400b) disposed at the base (200, 200a, 200b); wherein the fastening device (100, 110, 120) further comprising: the knob (500, 500a, 500b) comprising a spiral track (530, 530a, 530b); the engaging unit (400, 400a, 400b) comprising a guiding portion (430, 430a, 432b) coupled to the spiral track (530, 530a, 530b); and wherein the engaging unit (400, 400a, 400b) has a first position and a second position relative to the knob (500, 500a, 500b), the engaging unit (400, 400a, 400b) prohibits the spool (300, 300a, 300b) from rotating toward a releasing direction when the engaging unit (400, 400a, 400b) is at the first position, the engaging unit (400, 400a, 400b) allows the spool (300, 300a, 300b) to be rotated toward the releasing direction when the knob (500, 500a, 500b) is rotated toward the releasing direction and the guiding portion (430, 430a, 432b) moves relative to the spiral track (530, 530a, 530b) to allow the engaging unit (400, 400a, 400b) to switch to the second position, characterized in that, the fastening device (100, 110, 120) comprising: at least one retaining portion (410, 410a, 410b, 420, 420a, 420b, 430b); and the at least one retaining portion (410, 410a, 410b, 420, 420a, 420b, 430b) is coupled to the knob (500, 500a, 500b) or the base (200, 200a, 200b) to allow the engaging unit (400, 400a, 400b) to be remained at the first position or the second position. the knob (500, 500a, 500b) comprising a spiral track (530, 530a, 530b); the engaging unit (400, 400a, 400b) comprising a guiding portion (430, 430a, 432b) coupled to the spiral track (530, 530a, 530b); and wherein the engaging unit (400, 400a, 400b) has a first position and a second position relative to the knob (500, 500a, 500b), the engaging unit (400, 400a, 400b) prohibits the spool (300, 300a, 300b) from rotating toward a releasing direction when the engaging unit (400, 400a, 400b) is at the first position, the engaging unit (400, 400a, 400b) allows the spool (300, 300a, 300b) to be rotated toward the releasing direction when the knob (500, 500a, 500b) is rotated toward the releasing direction and the guiding portion (430, 430a, 432b) moves relative to the spiral track (530, 530a, 530b) to allow the engaging unit (400, 400a, 400b) to switch to the second position, characterized in that, the fastening device (100, 110, 120) comprising: at least one retaining portion (410, 410a, 410b, 420, 420a, 420b, 430b); and the at least one retaining portion (410, 410a, 410b, 420, 420a, 420b, 430b) is coupled to the knob (500, 500a, 500b) or the base (200, 200a, 200b) to allow the engaging unit (400, 400a, 400b) to be remained at the first position or the second position. at least one retaining portion (410, 410a, 410b, 420, 420a, 420b, 430b); and the at least one retaining portion (410, 410a, 410b, 420, 420a, 420b, 430b) is coupled to the knob (500, 500a, 500b) or the base (200, 200a, 200b) to allow the engaging unit (400, 400a, 400b) to be remained at the first position or the second position.