The skilled machinists evaluate exactly the tool changing time from observational information in cutting process. Such machining know-how gained through long experience may be regarded in a sense as fuzzy object. Recently, the study on the model representation of this know-how are progressed for making use of automatic working. In this paper, a rational way for the constructed model of evaluating the tool changing time is discussed. The proposed model gives the value of sharpness grade by weighing the observational information on fuzzy measure which the machinist's subjective characteristics in grading the tool changing time are identified. From the applications of model using fuzzy integral, it was found that the output of the model agreed approximately with the machinist's evaluation, and that the model became a very useful method for the monitoring by the in-process measurement.