Cognitive radio system consists of multiple wireless accesses that cover overlapping area, and cognitive terminals that use one or more of the wireless accesses simultaneously. In this paper, we present the architecture of the cognitive radio system that we proposed. In the proposed architecture, each cognitive terminal, that has multiple radio systems, operates with a single local IP address. Based on the proposed architecture, we have developed a simulator with EVDO, WiMAX and wireless LAN, and evaluated inter cognitive base station handover. From a result of simulation, it was found that it took 66 msec for the beginning of handover to the end.