PURPOSE: To reduce the weight of a jack by providing a hollow pin necking- processed from a molded leg part, a thin plate tongue piece or a thin plate, as a shaft, and engaging the hollow pin in a hole of a corresponding structural member.

CONSTITUTION: Molded leg parts 15, 17 and a thin plate tongue piece 13 overlap in a link range, a hollow pin 19 is necking-processed as a shaft from the molded leg parts 15, 17 and the thin plate tongue piece 13, and the hollow pin is engaged in a hole 18 of a corresponding structural member. For preventing the hollow pin 19 from being separated from the hole 18, a hollow pin end 20 projecting outward from the hole 18 is collared, so as to have the end diameter larger than that of the hole, and the connection of the link in a state of shape connection can be obtained. Therefore, an additional structural member, namely a shaft, is not required.