A communication system includes a division size determining unit configured to determine a division size when update data for an application that is executed by a first communication device is divided into a plurality of pieces of data based on band information indicating a band capable of being used for communication by the first communication device, a dividing unit configured to divide the update data into a plurality of pieces of data using the division size determined by the division size determining unit, and a relevant information generation unit configured to generate relevant information relating to the pieces of data divided by the dividing unit. In the communication system, a second communication device transmits the relevant information to the first communication device, and the first communication device receives the update data divided into the division size so as to perform update in accordance with the relevant information.