Compasses capable of wantonly fixing radius of drawn circle

The utility model discloses a pair of compasses capable of randomly fixing the radius of a drawn circle. A supporting structure with an inner arc-shaped sliding chute is additionally arranged on the middle upper parts of two legs of the existing compasses, and the size of the supporting structure can be fixed by a fixing screw and a fixing screw cap. An attaching pen is fixed on the legs by the fixing screw which can be slid in an arc-shaped slideway, and the supporting structure is fixed to the leg of the center of a circle. In addition, a long and thin tip of a tip end of the leg of the center of the circle is changed to a blunt tip, and errors can be reduced. The disadvantage that the two legs of the existing compasses are fixed unsteadily is overcome by the utility model.