To provide an arm storage mechanism capable of easily storing an arm without being loaded with a large stress and also stably retaining an expansion state of the arm when the arm is expanded.

An arm storage mechanism 10 includes an arm 20 held in an expansion state or a storage state, a storage means 30 rotatably fixed with an lower end to set the arm 20 from the expansion state to the storage state by rotation thereof, a rotating means 40 for rotating the storage means 30, a holding face 51 for holding such that the rotating means 40 does not rotate the storage means 30 by bringing into contact with the rotating means 40, and a holding means 50 for moving the holding face 51 to a position, bringing into contact with the rotating means 40 but not bringing into contact with the rotating means 40 when receiving an external force.