To provide a loading method capable of efficiently loading various sizes of existing containers.

In this loading method capable of loading so as to load and unload the empty containers by a loading/unloading device 6 provided on an under carriage 2, the two different sizes of the containers 5L, 5S are individually loaded onto the body, and the respective empty containers are matched so that the small-sized container 5S may be accommodated in the large-sized container 5L. A rear surface tailgate is made to open to the inside of the large-sized container loaded down on the ground, and the small-sized container is loaded down from the body by the loading/unloading device to be accommodated, thus unloading the large-sized container which accommodates the small-sized container between the ground and the body upper part by the loading/unloading device.