Particles in an accommodation chamber are also easily discharged while facilitating replacement of an atmosphere in the accommodation chamber with an inert gas. An EFEM includes a load port 4, a housing configured to define, in the housing, a transfer chamber closed by connecting the load port 4 to an opening provided in a partition wall, a supply pipe for supplying nitrogen to a transfer chamber, and a discharge pipe 49 for discharging a gas in the transfer chamber. The load port 4 includes an opening/closing mechanism 54 capable of opening and closing a lid 101 of a mounted FOUP 100, and an accommodation chamber 60 kept in communication with the transfer chamber via a slit 51b and configured to accommodate a part of the opening/closing mechanism 54. The discharge pipe 49 is connected to the accommodation chamber 60 to discharge the gas in the transfer chamber via the accommodation chamber 60.