PURPOSE: To eliminate a noise disturbance, and to execute welding with a high accuracy and at a low cost by providing an impedance signal equalization amplifier circuit, and always maintaining an output at a prescribed level even if a level of an impedance signal is veried.

CONSTITUTION: Even if a detecting value of the impedance of a welding arc is inputted to an impedance signal equalization amplifier circuit and a level of an impedance signal is varied, an output which is always maintained at a prescribed level is obtained. This equalizing impedance signal is inputted to a comparison discriminator which is required for determining a welding torch weaving end turning-back point, and subjected to a welding weaving width automatic control and a welding groove width automatic follow-up control. According to said welding profile detecting device, a noise disturbance is scarcely generated, and welding is executed with a high accuracy and at a low cost.