Anti-shock device for high frequency welding machines, wherein said welding machines comprise at least one oscillator in class C with a triode provided with a grid on the supply line, the triode being configured to power a resonant circuit which in turn powers mold holding plates (1, 2) of said welding machine; the anti-shock device comprising: a. a control unit connectable to a discharge sensor of the mold holding plates (1, 2) of the welding machine; b. a locking unit of the triode of the oscillator of the welding machine acting on the grid of the triode; said locking unit of the triode comprising a transformer which powers a voltage doubler rectifier bridge which in turn powers a battery of capacitors; said control unit being configured to: i. make a comparison with a preset sample value, ii. process the data received and when the resistance values between the plates decreases very quickly send a signal to said locking unit of the triode, said locking unit further comprising: - at least two IGBT type bipolar transistors in series adapted to connect the positive side of the rectifier bridge to earth; - a contact inserted in series between a grid resistance and earth; characterized in that said locking unit further comprises: - an ON-OFF contact for galvanic separation arranged in series between a grid resistance and said contact; - a third IGBT bipolar transistor, in parallel to the contact. a. a control unit connectable to a discharge sensor of the mold holding plates (1, 2) of the welding machine; b. a locking unit of the triode of the oscillator of the welding machine acting on the grid of the triode; said locking unit of the triode comprising a transformer which powers a voltage doubler rectifier bridge which in turn powers a battery of capacitors; said control unit being configured to: i. make a comparison with a preset sample value, ii. process the data received and when the resistance values between the plates decreases very quickly send a signal to said locking unit of the triode, said locking unit further comprising: - at least two IGBT type bipolar transistors in series adapted to connect the positive side of the rectifier bridge to earth; - a contact inserted in series between a grid resistance and earth; characterized in that said locking unit further comprises: - an ON-OFF contact for galvanic separation arranged in series between a grid resistance and said contact; - a third IGBT bipolar transistor, in parallel to the contact. i. make a comparison with a preset sample value, ii. process the data received and when the resistance values between the plates decreases very quickly send a signal to said locking unit of the triode, said locking unit further comprising: - at least two IGBT type bipolar transistors in series adapted to connect the positive side of the rectifier bridge to earth; - a contact inserted in series between a grid resistance and earth; - at least two IGBT type bipolar transistors in series adapted to connect the positive side of the rectifier bridge to earth; - a contact inserted in series between a grid resistance and earth; - an ON-OFF contact for galvanic separation arranged in series between a grid resistance and said contact; - a third IGBT bipolar transistor, in parallel to the contact.