PURPOSE: To improve the surface finishing accuracy by forming a spacer ring provided on a hub end part of a rotary peening apparatus provided with a large number of peening flaps around a hub of a large number of pin members which are attachable/detachable to/from a holding means of the hub end part and different in length.

CONSTITUTION: This rotary peening apparatus is radially provided with a large number of peening flaps 110 having peening parts 128... on its outer circumference on a circumference of a hub 100, and the hub 100 is provided with a guide 112 to hold a holding end 116 of each flap 110 in an attachable/detachable manner 116. The guide 112 is arranged along the circumferential surface of the hub 100 with intervals, and has a flap insertion port 114. A spacer ring 160 is provided to position a large number of flaps 110 with respect to the end part of the hub 100, the spacer 160 is provided with a large number of pin members of different height along the circumferential direction of a ring-like base member 194, and the pin members are fitted to a guide 112 as a holding means in an attachable/detachable manner.