[en] To provide for a more reliable operation of an accelerator and a higher accuracy in shaping the plateau of the main magnetic field, a device is suggested for synchronizing the synchrotron operation with the feeding circuit frequency. The device consists of a thyristor key connected parallel to the circuit consisting of an additional inductance and a resonance circuit capacitance, connected in series, that, together with the electric magnet, form the resonance circuit. The period of voltage across the electric magnet is regulated by varying the resonance circuit capacitance recharging level. To shape the magnetic field plateau, the positive voltage semiwave is shunted at a certain moment of time; whereas, for synchronizing with the feeding circuit, the time moment of shunting the negative semiwave of the voltage across the electric magnet is varied as a function of the difference between the voltages of the electric magnet and the circuit