1. An apparatus for detecting or predicting a breakage of a tool used in a machine tool, the apparatus comprising: cutting load detecting means for detecting a cutting load; means for obtaining at least one of three cutting load data by said cutting load detecting means, including a cutting time, an area of a cutting load waveform during cutting, and a maximum absolute value of a slope of a drop in a cutting load during the cutting, in a machining cycle, as a load state value in a current machining cycle; means for updating and obtaining a moving variable threshold based on the load state value calculated in a machining cycle before the current machining cycle; and means for comparing the load state value in the current machining cycle with the moving variable threshold to determine an abnormal condition of the tool.