To fix an open state without integrating a notch by inserting the insertion piece of a side leaf to an insertion groove, rotationally fixing a pivot hole by an eyelet and bringing the ground end of a circumferential notch and the insertion groove into contact.

The circumferential notch 7 whose center is the pivot hole 6 is made, the top end 10 is positioned right above the pivot hole 6 in a closed state and the ground end 11 is provided on a part positioned right below the pivot hole 6 in an opened state. Assembly is performed by inserting the insertion piece 8 to the insertion groove 9 of a B leaf 3. The insertion groove 9 is opened large since the lower part of the insertion groove 9 is cut off, the insertion piece 8 is easily slid from the lower part and inserted, the positions of the pivot holes 6 are overlapped in the state of inserting the insertion piece 8 from the front and back of the B leaf 3 and fixed by passing through the eyelet. Since the top end 10 of the circumferential notch 7 is brought into contact with the insertion groove 9 in the closed state, a C leaf 4 is not rotated to a left side which is a closing direction and fan leaves 1 are prevented from going too far and being shifted from the closed state. The spread state of the fan leaves 1 is fixed without being opened any more since the ground end 11 of the circumferential notch 7 is brought into contact and held in the insertion groove 9.