To make attachment of wheels easy with vibrations occurring to a container on turning of the wheels reduced, and to restrain abrasion on the container arising from turning of the wheels.

A shaft 19 is provided at the lower part of a container 11 as an integral part, and first and second recesses 20 and 21 are provided at the shaft 19. A detent 28 and a notch 29 are provided at a cylindrical part 27 of a wheel retainer 25. A wheel 15 is assembled to the shaft so that the cylindrical part 27 of the wheel retainer 25 is put between the shaft 19 and the boss of the wheel 15. The detent 28 is engaged with the first recess 20 while the notch 29 is engaged with the second recess 21, and thereby the wheel retainer 25 can be held to the shaft 19.