An exchangeable filter of a treatment device has a housing with a housing pot and a housing cover connected to the open side of the housing pot. The exchangeable filter is connectable to a connecting head of the treatment device with a bayonet-type connecting device. The connecting device has a housing connecting part on the housing interacting with a head connecting part of the connecting head for connecting the connecting device. The housing has an inlet for a fluid to be treated connectable to a supply conduit of the treatment head and an outlet for the treated fluid connectable to a discharge conduit of the treatment head. The housing pot has a rim at the open side of the housing pot. The rim radially outwardly surrounds the housing connecting part and axially projects past the housing connecting part in a direction away from the housing bottom.