PURPOSE: To obtain a small and light engine-driven arc welding machine which has simple structure, and uses an inexpensive polyphase induction generator by constituting one pole of one field winding and armature windings of the number equal to the number of phases on the internal surface of a stator and, at the same time, forming salient poles of the number equal to the number of poles on the peripheral edge of a rotor.

CONSTITUTION: When a four-pole three-phase generator 1 is used, three phases of armature windings a1-a4, b1-b4, and c1-c4 and four poles of field windings f1-f4 are wound in 12 grooves m1-m12 provided on the inner peripheral surface of a stator 2 at regular intervals and four equally divided salient poles 31-34 are provided on a rotor 3. Then three-phase DC voltages respectively having phase differences of 120° against each other are generated across the armature windings a1-a4, b1-b4, and c1-c4 by supplying DC currents to the windings f1-f4 so that tooth sections t1, t2, and t3 and t7, t8, and t9 can become N poles and tooth sections t4, t5, and t6 and t10, t11, and t12 can become S poles.