When the capacity availability of buffer memory provided to an output port of a frame to be transferred is exceeding a predetermined value, a crossbar switch is used for path change of the frame. When the capacity availability of the buffer memory of the output port is the predetermined value or lower, the frame is written into shared memory. Then, the frame is read from the shared memory for transfer to the output port. By selectively performing frame transfer using the crossbar switch and frame transfer via the shared memory, the effects can be reduced even if the port buffer overflows, and the writing throughput can be favorably improved.