To suppress processing costs to achieve the stable accuracy of processing.

The finishing processing device is used to carry out finishing processing on a funnel-like surface formed at an opening of a hole. The finishing processing device includes a grinding unit 1 which finishes the wall surface of the hole, and a drive unit 3 which moves the grinding unit 1 along a rotation axis P while rotating the grinding unit around the rotation axis P along the axis of the hole. The grinding unit 1 is so disposed that it can change its posture between a position at which a widening angle with respect to the rotation axis P is larger and a posture at which the widening angle is smaller. When an intrusion amount into the hole is small, the grinding unit 1 takes a posture for a larger widening angle so that the grinding unit 1 comes in contact with this side of the funnel-like surface. When the intrusion amount into the hole is large, the grinding unit 1 takes a posture for a smaller widening angle so that the grinding unit 1 comes in contact with the deeper side of the funnel-like surface.