PERFECT CIRCLE HOLDING DEVICE

PROBLEM TO BE SOLVED: To provide a perfect circle holding device capable of holding a shape of a segment in a curved driving section with uniform press force and to provide a perfect circle holding device advantageous in space and manufacturing costs.SOLUTION: A perfect circle holding device (10) holds a shape of a segment (S) covering, in a ring shape, an inner surface of a tunnel excavated by a shield excavating machine (1) by pressing the inner surface, and includes: a pair of right and left moving carriages (20) capable of moving on a support member (3) extending in parallel with an axis of the shield excavating machine (1); a pair of right and left extending/contracting columns (30) which are stood on the pair of moving carriages (20) and can extend and contract vertically; an upper arch (40) which is constructed over between upper end parts of the pair of extending/contracting columns (30); a pair of right and left pin coupling mechanisms (50) which couple the upper end parts of the pair of extending/contracting columns (30) to the upper arch (40) with pins rotatably on axes parallel with the axis of the shield excavating mechanism; and a pair of right and left energizing mechanisms (60) which energize the pair of right and left extending/contracting columns (30) in a perpendicular posture.