Camshafts are mostly quenched at 8 kHz MF, and camshafts produced in single or small quantities are also quenched at 250 kHz. If the width of each quenching part is the same, it can be quenched by an inductor. When the width of the quenched portion is different, one or several inductors may be used for quenching depending on the situation. The high frequency quenching sensor of the camshaft can be either circular or contoured.