The invention concerns a head for detecting a conductivity defect in a conductive or magnetic part comprising at least one concentrator (50) of the flow of an excitation magnetic field having a first end (58) through which exit mainly the field lines (62) prior to the penetration of said lines into the part (4), and at least one second end (60) through which enter mainly the field lines from the part. The first and second ends both face the part (4) to limit evanescence of the lines in the air.
