An unmanned conveying device for a clean room is capable of restraining a spontaneous oxide film from growing in case that an unmanned carriage is obliged to stop for a long time due to its own cause of a cause at a destination spot while it conveys a semiconductor wafer from one spot to the destination spot. It is a first aspect of the invention to provide the unmanned conveying device which is self-propelled for conveying an object from a ground facility to a destination spot while loading an object to be conveyed thereon, characterized in that the object is accommodated in a container and the container is connected to an inert gas reservoir through a gas supply passage so that the atmosphere in the container can be replaced by a nitrogen gas. It is a second aspect of the invention to provide an unmanned conveying device for a clean room provided with a container for accommodating an object to be conveyed therein, the container being connected to an inert gas reservoir through a gas supply passage so that the air in the container can be replaced by a nitrogen gas, characterized in that the unmanned conveying device has a coupler unit mounted thereon and connected to the gas supply passage and the inert gas reserving source is located on the ground and connected to a coupler unit of a coupler device on the ground through a pipe and the gas supply passage is connected to the inert gas reservoir through both coupler unit.