Disclosed is a wire breakage detection device of a diamond wire cutting machine. The wire breakage detection device of the diamond wire cutting machine comprises a tensioning mechanism, a wire windingbeam, a heavy hammer, a proximity switch and a pull wire. The heavy hammer is hinged to one end of a driving shaft of the diamond wire cutting machine. The wire winding beam, the proximity switch andthe heavy hammer are located at the same end of the driving shaft, and the tensioning mechanism is located at the other end of the driving shaft. The head end of the pull wire is led out of the tensioning mechanism, then surrounds the wire winding beam and is connected with the hinge-free end of the heavy hammer. In the initial state, the heavy hammer gets close to the induction region of the proximity switch under the action of the pull wire; and after the pull wire is broken, the heavy hammer gets away from the induction region of the proximity switch under the action of the gravity. By theadoption of the wire breakage detection device, the factor that the interference with the detection result happens due to the fact that water conducts electricity can be eliminated, and therefore a system is prevented from sending wrong alarm signals out.