This category of equipment is known as “Ground Support Equipment” (see Wikipedia article).
This includes a variety of utility vehicles, including refuelers, dollies, chocks, buses and more.
However, the one you’re after is the Belt loader:
Belt loaders are vehicles with conveyor belts for unloading and
loading of baggage and cargo on aircraft. A belt loader is positioned
at the door sill of an aircraft hold (baggage compartment) for the
operation. Belt loaders are used for narrow body aircraft and bulk
hold of wide body aircraft. Baggage stored without containers is known
as bulk loading.
I just found it in Ground support equipment:
It is called “Belt loader”.
Credit:stackoverflow.com‘