A multiplex apparatus includes a plurality of systems configured to be connected to each other by links. Each of the plurality of systems includes a CPU, a pseudo legacy device and a legacy device. The pseudo legacy device is configured to be electrically connected to the CPU. The legacy device is configured to be electrically connected to the pseudo legacy device. The pseudo legacy device includes a request buffer and a pseudo operator. The request buffer is configured to store a request when the CPU sends the request through the pseudo legacy device to the legacy device. The pseudo operator is configured to execute an emulation with regard to the legacy device based on the request, and store the emulation result including an inside status of the legacy device.