A switch device includes a receiving buffer, a switching processing unit, a determining unit, a generating unit, and a transmitting unit. The receiving buffer receives a data packet from a communication device. The switching processing unit stores the data packet received by the receiving buffer to one of a plurality of output queues provided for respective transmission ports based on the destination. The determining unit determines whether the amount of data in the output queues is equal to or more than a predetermined threshold. If the determining unit determines that the amount of data in any one of the output queues is equal to or more than the predetermined threshold, the generating unit generates a notifying packet for notifying that congestion has occurred. The transmitting unit transmits the notifying packet generated by the generating unit to another switch device.