A fastening device includes a case, a spool and a knob. The case includes a housing and a base. The housing includes a receiving space and two side holes communicated with the receiving space. The base is detachably connected to the housing. The base includes a continuous wall, and the continuous wall surrounds a lower edge of the housing after the base is connected to the housing. The spool is received in the receiving space and configured for a lace passing through the side holes to be wound therearound. The knob is disposed on the case. Rotating the knob relative to the case in a fastening direction causes the spool to rotate in the fastening direction for fastening the lace.