The present invention provides a machine tool which is adapted to detect the end of the service life of a spring of a clamp unit for fixing a tool to a spindle for systematic replacement of the spring. The machine tool comprises a clamp unit (47) for fixing a tool in a taper hole provided in a spindle, and a controlling section (63) for controlling the operation of the clamp unit. The clamp unit (47) includes a holder for holding a holder portion of the tool, a driving rod coupled to the holder, a driver for moving the driving rod along an axis thereof, and a spring for biasing the driving rod in one direction along the axis thereof. The machine tool further comprises a service life end detecting section (11) for counting the number of times of actuation of the clamp unit (47) and, when the count of the number reaches a predetermined reference actuation number, judging that the service life of the spring ends. With this arrangement, maintenance can systematically be carried out by detecting the end of the service life of the spring.