A decider decides whether a predetermined period of time has elapsed after a last one of first packets was received and a timeout thereby occurs. A second packet having a size of data greater than a size of data placed in each of the first packets is produced from a number of the first packets, the number being a first threshold value. Another decider decides, when the predetermined period of time has elapsed, whether a number of times by which the predetermined period of time has successively elapsed exceeds a second threshold value which is a permitted number of times of the timeout. A processing unit sets, when the second threshold value is exceeded by the number of times that the predetermined period of time has successively elapsed, the first threshold value so as to decrement the number of the first packets to be used to produce the second packet.