Main spindle abnormity detection device for machine tool and method of detecting main spindle abnormity

A main spindle abnormity detection device and a method of detecting a main spindle abnormity are provided to daily diagnose main spindle abnormities using a cheap and short-time method. An abnormity detecting part of the device includes a rotation speed detection unit (a rotation speed detector and a rotation speedometer measuring part) for detecting the rotation speed of the main spindle; a reach time estimation unit (a rotation speed change estimation and calculation part) configured to estimate a reach time in which the rotation speed of the main spindle reaches a predetermined rotation speed threshold using a non-linear model based on a rotation speed of the main spindle detected at a start of an inertia operation and a rotation speed of the main spindle detected after an elapse of preset measurement time from the start of the inertia operation; and a determining unit (a main spindle abnormity determining part) configured to compare the reach time estimated by the reach time estimation unit with a preset