A communication system includes: storage to store location information of each of a plurality of devices capable of wireless multi-hop communication, site configuration information including location and size information of an obstacle present at a site of the plurality of devices, and communication quality information between devices; a determination unit determines whether a repeater needs to be added for each of the plurality of devices, based on communication quality information; and a decision unit calculates an expected value related to attenuation of received power between the first and second devices caused by the obstacle, and decides a location for the determination unit to add the repeater based on location information of the first device determined, location information of the second device different from the first device and communicated with the first device through the repeater, the communication quality information between the first and second device, and the site configuration information.