A communication aggregation system according to an exemplary embodiment of the invention includes a plurality of devices (3) to (6) that transmit a larger amount of data when an abnormality is found compared with the amount of data transmitted in normal times, a gateway device (1) that communicates with devices included in a first group out of a plurality of devices, a gateway device (2) that communicates with devices included in a second group, and a control device (7) that, when the amount of data transmitted from some device increases due to detection of an abnormality and a difference in processing loads between the gateway devices exceeds a first threshold, changes a group to which at least one device out of the plurality of devices (3) to (6) belongs so that a difference in the processing loads falls below a second threshold.