A mobile agent is a one of important platform for applications for coming ubiquitous world. Many different kinds of mobile agent platforms have been developed. However, agents from one agent platform are generally not able to migrate into another agent platform. As a solution to this problem, we propose an interoperability concept using an Incarnation agent. The concept realizes logical mobility within different kinds of agent platforms. The Incarnation agent extracts an agent's procedures and status, compiling them into agent platform independent format and then re-compiling them to target agent platform format, thus enabling the process to continue. The Incarnation agent also has autonomy for interoperability. It manages complex migration for interoperability, so agent's procedure can be described in simple mobile model. Moreover, the Incarnation Agent modifies agent's procedures as applicable to facilities of target agent platform. This paper also reports an interoperability middle-ware and its examination. The middle-ware is a foundation of realizing the Incarnation Agent, and the response time and network traffic overheads by the interoperability middle-ware has been measured.