An adjusting device for tightening or loosening a lace is provided. The adjusting device includes a base, a knob and a releasing unit. The releasing unit is disposed in the base and the knob, and the knob is used for winding the lace. The releasing unit and the knob are pivotally disposed in an accommodating space. The releasing unit includes at least one elastic arm corresponding to an annular tooth in the knob. The releasing unit can be raised or lowered on the base. When the releasing unit is raised, the knob can be freely rotated; and when the releasing unit is lowered, the rotation of the knob is limited in a releasing direction.