Machine tool and control device for machine tool

A control device for a machine tool including a driver that drives a main spindle for holding a workpiece rotatably, a servo motor that drives a tool for machining the workpiece held on the main spindle, and a power source that supplies electric power to at least the driver and the servo motor, the control device comprising:

• a current detector that detects a current value to be inputted into the servo motor;
• a storage that stores an upper limit of the current value to be inputted into the servo motor;
• and
• a controller that controls the servo motor to execute driving control of the tool, wherein
• when a current value detected by the current detector exceeds the upper limit of the current value immediately after starting the main spindle, the controller changes an acceleration/deceleration time constant from a first time constant to a second time constant that is lower in power consumption than the first time constant, thereby controlling the servo motor.