To provide a thin sheet ring forming device capable of machining a press ring so as to obtain the stable forming dimensions.

This thin sheet ring forming device is provided with a table 14 turnable around a support shaft 13, a clamp 15 capable of fixing a press ring 8 having a flange part projected inwardly in the radial direction to the table 14 so that the center of the radius is agreed with the turning center of the table 14, a first block 16 capable of being locked to the support shaft 13, a lever 17 in which a base end part is pivotably supported by a first block 16 and a tip part is supported by a positioning block 35 in the vicinity of the table 14, a second block 18 mounted on an intermediate part of the lever 17, and a press roller 19 which is pivotably supported by the second block 18 and abutted on the flange part of the press ring 8. Then the flange part of the press ring 8 is pressed by a press roller 19.