PURPOSE: To provide a convenient spindle device which is capable of rotating a spindle within a range not exceeding an allowable rotational speed both rapidly and accurately.

CONSTITUTION: A radial vibration damping displacement of a spindle 2 is detected with a sensor portion 5, as the tip of the spindle 2 or a portion of a tool 4 is vibrated due to a vibratory means, such as a hammer. A detection result of the sensor portion 56 is sent to an allowable rotational frequency arithmetic portion 7 via an amplifier 6. In the allowable rotational frequency arithmetic portion 7, an allowable rotation frequency (f) of the spindle 2 is computed on the basis of the detection result (a radial vibrator damping displacement of the spindle 2) of the sensor portion 5. The arithmetic result is then outputted to a motor drive power supply 8. The motor drive power supply 8 thus drives the motor within a range not exceeding an allowable rotational frequency (f) thereby rotating the spindle 2.