PURPOSE: To simplify the tight fitting of rims in a tire, by providing a hydraulic jack with a holding cylinder and using the jack and the cylinder to push the rims toward each other.

CONSTITUTION: A holding cylinder 20 is coupled to the holding body 12 of a hydraulic jack 10 by fitting the openings 22 of a holding cylinder 20 with the engagement rods 13 of the jack 10. A bar 30 is inserted into the openings 21 of the holding cylinder 20 and placed on the top of a piston 14 in the body 12. A rim 40 is placed on the bar 30 around the holding cylinder 20 so that the outside of the rim 40 is located face-down. A tire 50 and another rim 40 are placed around the holding cylinder 20. Another bar 30 is then inserted into the openings 21 and put on the latter rim 40. When the jack 10 is actuated to move the piston 14 up, some members are elevated and the latter bar 30 comes into contact with the upper edges 21a on the openings 21 and stops moving up. The piston 14 is moved up further so that the rims 40 are tightly fitted in the opening 51 of the tire 50.