PURPOSE: An automatic control apparatus of a scarfing machine is provided to allow a scarfing work to be smoothly performed by automatically setting a scarfing speed and a scarfing thickness on the basis of a surface temperature of a slab detected before the scarfing work. CONSTITUTION: The scarfing machine basically comprises a transfer roller(100), a strike roll(104), a first and a second pinch roll(108,112), a smog hood(200), a first and a second scarfing units(306,308), an edge unit(310), which are same with those of conventional scarfing machine. A positioner(124) supporting the transfer roller is provided with an information detecting part(400) capable of measuring the width and the surface temperature of a slab. The information detecting part consists of a width detecting sensor and a temperature detecting sensor. A pre-heat position detecting part(500) is installed on the inner wall surface of the smog hood, so as to accurately positioning the head of the slab to a pre-heat position of the scarfing machine. A pre-heat detecting part(600) is installed on the lower end of the first and the second scarfing units, so as to detect the pre-heat condition of the slab and, at the same time, to detect the distal end of the slab.