PURPOSE: To discover melting abnormality in an early period by measuring the supply voltage value from a TIG power source and judging the melting abnormality when the value exceeds a prescribed upper limit value or lower limit value.

CONSTITUTION: The remelting treatment of a cam 4 is executed by moving a TIG torch 3 having the TIG power source 1 and a tungsten electrode 2 back and forth in an arrow A direction and displacing the torch to follow up at prescribed intervals in an arrow B direction. A cam shaft 5 rotates the cam 4 and a position detector 6 detects the position of the cam 4. An ammeter 7 and a voltmeter 8 are mounted to the TIG power source 1 and the voltmeter 8 can detect the upper limit value and the lower limit value. A melting shear droop 13 is generated on the end face of the cam 4 when the central point of the forward and backward movements of the electrode 2 deviates from a center line 11. The remelting region diminishes when the spacing R between the electrode 2 and the surface 10 of the cam 4 is shorter than the prescribed distance. The voltage of this time is lower than the lower limit value. The defect of the remelting treatment is discovered by measuring the voltage.