The invention relates to the field of grinding machine machining, in particular to a power source power supply device of a grinding machine. A three-phase four-wire power supply circuit is connected with a magnetizing and demagnetizing device and a plurality of contactors. The first contactor is connected with a grinding wheel motor. The magnetizing and demagnetizing device comprises an undercurrent relay. One end of a normally-closed node of the undercurrent relay is connected with direct current 24V, and the other end of the normally-closed node passes through a button K and then is connected with a first contactor KM1 coil and a 24 V ground wire. The undercurrent relay is additionally arranged to control start and stop of a grinding wheel motor, and the accidents that workpieces fly andbruise equipment and personnel are avoided.