An abnormality detection apparatus for a tool (11) is described for judging abnormalities of a tool by a uniformly set threshold value in relation to a cutting load even in a machining process wherein a feed rate changes every moment. The abnormality detection apparatus for a tool (10 or 21) comprises cutting load detecting means (8) to detect a cutting load on the basis of an electric current for driving that is output to a feed drive system (14) and/or an electric current for driving that is output to a spindle drive system (15), feed load estimating means (12) to estimate a feed load according to the feed rate wherein the feed load depends on the feed rate, tool load detecting means (11) to pick out a load component depending on the tool by reducing the feed load data estimated by the feed load estimating means (12) from the cutting load data detected by the cutting load detecting means (8), and abnormality judging means (13) to judge whether the tool is in an abnormal condition or not on the basis of the load data picked out by the tool load detecting means (11). The abnormalities of the tool can be judged by the uniformly set threshold value on the basis of the tool load wherefrom the feed load that fluctuates upon the feed rate has been removed.