In a load port apparatus, a door driving mechanism that supports a door through a communication opening portion leading to a mini-environment is housed in a housing chamber that is in communication with the mini-environment through the communication opening portion. Exhaust opening portions are provided in the upper portion of a wall of the housing chamber that is opposed to the communication opening portion and a bottom wall of the housing chamber. Thus, gas passages from the mini-environment to the housing chamber and then to the external space are formed. Thus, dust in the load port apparatus is removed.