Disclosed is a session control method in a Converged Internet Protocol (IP) Messaging (CPM) server for supporting a CPM session between a first client subscribing to a CPM service and a second client not subscribing to the CPM service, the session control method includes, after the CPM session is initiated between the first and second clients through the CPM server and an Interworking Function (IWF), receiving a session modification request message including specific media from the first client; sending the session modification request message including the specific media to the IWF through the initiated CPM session; and receiving a response message from the IWF, the response message including a reason for a rejection of the session modification request message including the specific media.