A rotation restricting device for restricting the rotation of a rotating part with respect to a base part, comprising a stopper supported so as to be capable of rotating around an axis of rotation of the base part, a lock mechanism capable of switching between a state preventing and a state allowing the rotation of the stopper with respect to the base part, a first block provided on the rotating part and capable of moving between a position interfering with and a position not interfering with a rotation path of the stopper, and a second block provided on the rotating part and capable of moving between a position interfering with and a position not interfering with the rotation path of the stopper. In a state where the rotation of the rotating part with respect to the base part is not restricted, both the first block and the second block are in the position interfering with the rotation path of the stopper, and the stopper is positioned between the first block and the second block.