A method and apparatus is provided of detecting tool abnormality in a machine tool. Permissible minimum and maximum values of load current in a real cutting section are determined for a spindle motor and a servomotor during normal operation of the machine tool. The load current of the spindle motor and the servomotor is measured while the machine tool is operated. The load current measured in a real cutting section other than a non-cutting section is extracted by way of filtering the load current measured. A judgment is made as to whether the extracted load current is within a range between the minimum and maximum values. Occurrence of the tool abnormality is confirmed if the extracted load current falls outside the range. This enables the machine tool to detect not only overload condition due to excessive wear of a tool but also non-load condition induced by a tool breakage.