A transfer chamber is provided between a processing unit for performing a predetermined process on a target substrate to be processed in a depressurized environment and an atmospheric maintaining unit for maintaining the target substrate in an atmospheric environment to transfer the target substrate therebetween. The transfer chamber includes a chamber main body for accommodating the target substrate, a gas exhaust unit for exhausting the chamber main body to set the chamber main body to the depressurized environment, and a gas supply unit for supplying a predetermined gas to the chamber main body to set the chamber main body in the atmospheric environment. Further, in the transfer chamber, an ionization unit is provided outside the chamber main body, for ionizing the predetermined gas and an ionized gas supply unit is provided to supply the ionized gas generated by the ionization unit to the chamber main body.