PURPOSE: To machine the internal peripheral surface of a cylinder into a circle by reproducing the condition at the time of finishing a circle by finishing the internal surface of a cylinder by means of the tool of an internal surface finishing tool machine in the state that a dummy head is fixed to the cylinder.

CONSTITUTION: A dummy head 10 is fixed to a cylinder block 1, and joint strain S, which is same as that in the state that a cylinder 8 is fixed, is kept generated in the thick wall section 4 of the upper section of a cylinder 2. The circle of a cylinder internal surface 3 is reproduced by finishing the internal peripheral surface 3 of the cylinder 2 in this state even in the case of replacing the dummy head 10 with the cylinder head 8. Therefore, joint strain 8 does not bring about ill effect.