A fastening device , comprising: a base ; a spool disposed at the base and a lace wound around the spool ; a knob disposed at the base ; and an engaging unit disposed at the base ; wherein the fastening device further comprising: the knob comprising a spiral track ; the engaging unit comprising a guiding portion coupled to the spiral track ; and wherein the engaging unit has a first position and a second position relative to the knob , the engaging unit prohibits the spool from rotating toward a releasing direction (A1) when the engaging unit is at the first position, the engaging unit allows the spool to be rotated toward the releasing direction (A1) when the knob is rotated toward the releasing direction (A1) and the guiding portion moves relative to the spiral track to allow the engaging unit to switch to the second position, characterized in that , the fastening device comprising: at least one retaining portion ; and the at least one retaining portion is coupled to the knob or the base to allow the engaging unit to be remained at the first position or the second position. a base ; a spool disposed at the base and a lace wound around the spool ; a knob disposed at the base ; and an engaging unit disposed at the base ; wherein the fastening device further comprising: the knob comprising a spiral track ; the engaging unit comprising a guiding portion coupled to the spiral track ; and wherein the engaging unit has a first position and a second position relative to the knob , the engaging unit prohibits the spool from rotating toward a releasing direction (A1) when the engaging unit is at the first position, the engaging unit allows the spool to be rotated toward the releasing direction (A1) when the knob is rotated toward the releasing direction (A1) and the guiding portion moves relative to the spiral track to allow the engaging unit to switch to the second position, characterized in that , the fastening device comprising: at least one retaining portion ; and the at least one retaining portion is coupled to the knob or the base to allow the engaging unit to be remained at the first position or the second position. the knob comprising a spiral track ; the engaging unit comprising a guiding portion coupled to the spiral track ; and wherein the engaging unit has a first position and a second position relative to the knob , the engaging unit prohibits the spool from rotating toward a releasing direction (A1) when the engaging unit is at the first position, the engaging unit allows the spool to be rotated toward the releasing direction (A1) when the knob is rotated toward the releasing direction (A1) and the guiding portion moves relative to the spiral track to allow the engaging unit to switch to the second position, characterized in that , the fastening device comprising: at least one retaining portion ; and the at least one retaining portion is coupled to the knob or the base to allow the engaging unit to be remained at the first position or the second position. at least one retaining portion ; and the at least one retaining portion is coupled to the knob or the base to allow the engaging unit to be remained at the first position or the second position. <EOS>