A heavy-object loading jig has a slide plate provided on the upper end portion of a lifting drive means and a mounting plate for mounting a heavy object thereon. Between the slide plate and the mounting plate is disposed a rolling member which allows the mounting plate to move in any horizontal direction within a limited range. The lifting drive may include: a circular cylinder vertically extending with the upper end thereof opened; a cylindrical member which is integrally secured to the inner lower end portion of the cylinder and defines an annular cylinder chamber between the same and the inner surface of the cylinder; a ring-shaped piston slidably received in the cylinder chamber; and a cylindrical rod which is formed integral with the piston and is projected beyond the upper end of the cylinder and further has the slide plate secured to the upper end portion thereof. The rod may be provided on the upper end portion thereof with a shock absorber which is able to abut against the upper end of the cylindrical member. Further, a cam structure for guiding the mounting plate to a fixed position when it is lowered may be provided between the cylinder and the mounting plate.