This study, the action of molten metal in the kerf using oxygen and an assist gas was observed with the high speed digital CCD camera. The ejection of molten metal is changed direction in every 2ms. Case of the optimum condition speed cutting (1800mm/min), the molten metal moves straight down to bottom of the kerf. Case of the high speed cutting (2800mm/min), case of the mass molten metal stays in the kerf, dross appeared underneath the workpiece. And case of ejection angle is over the 45 degree, dross appeared underneath the workpiece. Mass molten metal and small molten metal is every pulsed.