A communication apparatus is provided. The communication apparatus includes a first unit for performing data communication using a bandwidth reservation type transmission area constituted by a plurality of time-divided time slots via a power line to which an alternating-current voltage is supplied. A second unit is connected to the first unit, for securing a vacant time slot out of the plurality of time-divided time slots. A third unit is connected to the first unit, for securing a time slot out of the plurality of time-divided time slots when incapable of securing the vacant time slot, the secured time slot being used in common by a first communication system used by the communication apparatus and a second communication system different from the first communication system, the second communication system using the same communication procedure as the first communication system.