PURPOSE: To improve simplification and reliability of the operation by enabling a front wheel frame part, a rear wheel frame part and a connecting frame as a strength member for connecting them to each other to be easily disassembled and assembled without using any tool.

CONSTITUTION: A front wheel frame part 1, a rear wheel frame part 2 and a connecting frame 3 are provided, and connecting flanges 35, 36 fixed together with reinforcing bars 32, 33 are provided on both ends of a connecting bar 31 for forming the main constituent of the connecting frame 3. Respective connecting flanges 35, 36 are made to be brought in close contact with connecting flanges 131, 233 provided on the front and rear frames 1, 2 sides by taking stoppers 132, 234 as the guides and joined by a manual screw mechanism. At this time, the connecting flanges 233, 35, and the connecting flanges 131, 36 are brought in contact with each other on their flat surfaces and positioned, and the excessive three-dimensional load is supported by stoppers 234, 132 fixed on respective connecting flanges 233, 131.