To strengthen rigidity of an unfolding mechanism by sliding a fitting part of a latch pin of latch mechanisms to one side of shaft parts and rotary parts, bringing the fitting part near to an unfolding position, storing/fitting the fitting part in/to fitting holes, and completing unfolding operation.

Second to fourth joining parts 17, 18, 19 are stored in fitting holes 173, 183, 193 of shaft parts 171, 181, 191 by being brought near to an unfolding position by sliding a guide ball 232 of a fitting part 231 of a latch pin 23 of respective latch mechanisms 21 by rotating the rotary parts 172, 182, 192 in the unfolding direction in a state of causing a dimensional error by thermal deformation or the like in the shaft parts 171, 181, 191, the rotary parts 172, 182, 192, first to third link members and support parts 11, 12. The fitting holes 173, 183, 193 of the shaft parts 171, 181, 191 are fitted to the fitting part 231 of the latch pin 23 to complete unfolding operation.