PURPOSE: To provide the internal grinding machine which can surely detect its abnormality.

CONSTITUTION: A sizing means 1 detects each run-out in the radial direction of two positions faced to each other in the inner surface of a work, and outputs signals A and B representing each run-out. The signals A and B from the sizing means 1 are amplified by an amplifier 2, and the A/D conversion of the amplified signals A and B from the amplifier 2 is performed by a signal processing unit 3. The subtraction section 4a of a personal computer 4 computes the difference in the signals A and B from the signal processing unit 3, the A/D conversion of which has been performed, and concurrently the judging section 4b of the personal computer 4 judges whether or not its subtraction signal (A+B) is equal to or more than a specified upper limit value. And when the subtraction signal (A+B) is found to have been equal to or more than the specified upper limit, the judging section 45 judges that the action is abnormal, and the suspension section 4d of the personal computer 4 then outputs a suspension signal.