PURPOSE: To simplify the constitution, to miniaturize the structure, and to realize the reliable and sure action control by providing a locking means where a frame structure is developed from the folded position to the developing position, and the folded member is locked in an approximately straight manner in the condition the folded member is turned from the first position to the second position around the axis of turning.

CONSTITUTION: A locking claw 16 is turnably provided on a first member 10a, and a spring member 17 is locked to this locking claw 16 so as to give the spring force counterclockwise. A part 20 to be locked is provided on a second member 10b corresponding to the locking claw 16 of the first member 10a. A position regulating device connects each end part of the folded member 10 to each other across the axis 11 of turning of the folded member 10 through a wire member 15 and a tension spring member 14, and the energizing force of the tension spring member 14 is applied in an interlocking manner with the developing action at the folded position through the wire member in an interlocking manner with the developing action so that the energizing force of the tension spring member 14 may not be applied.