A routing control method in an optical packet switching network including a plurality of optical packet switches. Each optical packet switch has a plurality of output ports used for sending packets to other optical packet switches, respectively. The method particularly includes a step of, in a one optical packet switch, monitoring congestion conditions at its output ports, a step of, in the one optical packet switch, transferring packets to be stored in a one output port that is judged in the monitoring step as in congestion, to other output port that is judged in the monitoring step as not in congestion, a step of, from the one optical packet switch, sending the packets as reflection packets via the other output port to an other optical packet switch corresponding to the other output port, and a step of, from the other optical packet switch, returning the reflection packets to the one optical packet switch.