A communication system comprising a femto-cell base station for defining a predetermined communication area, a relay device (60; 70) for receiving a message transmitted from said femto-cell base station, and a management device (40; 50) for managing an IP address of said relay device (60; 70), wherein: said relay device (60; 70) comprises a CS (Circuit Switching) -dedicated relay device used for CS services and a PS (Packet Switching) -dedicated relay device used for PS services, said management device (40; 50) comprises a first management device for managing an IP address of said CS-dedicated relay device, and a second management device for managing an IP address of said PS-dedicated relay device, and said femto-cell base station comprises: first establishing means for acquiring the IP address of said CS-dedicated relay device from said first management device, connecting to said CS-dedicated relay device based on the acquired IP address of said CS-dedicated relay device, and establishing a first IPsec Tunnel between said femto-cell base station and said CS-dedicated relay device; and second establishing means for acquiring the IP address of said PS-dedicated relay device from said second management device through said first IPsec Tunnel, connecting to said PS-dedicated relay device based on the acquired IP address of said PS-dedicated relay device, and establishing a second IPSec Tunnel between said femto-cell base station and said PS-dedicated relay device, wherein: said femto-cell base station acquires an IP address of said second management device from said CS-dedicated relay device when the first IPsec Tunnel is established between said femto-cell base station and said CS-dedicated relay device, queries said second management device for the IP address of said PS-dedicated relay device through said first IPsec Tunnel based on the acquired IP address of said second management device, and acquires the IP address of said PS-dedicated relay device from said second management device through said first IPsec Tunnel. said relay device (60; 70) comprises a CS (Circuit Switching) -dedicated relay device used for CS services and a PS (Packet Switching) -dedicated relay device used for PS services, said management device (40; 50) comprises a first management device for managing an IP address of said CS-dedicated relay device, and a second management device for managing an IP address of said PS-dedicated relay device, and said femto-cell base station comprises: first establishing means for acquiring the IP address of said CS-dedicated relay device from said first management device, connecting to said CS-dedicated relay device based on the acquired IP address of said CS-dedicated relay device, and establishing a first IPsec Tunnel between said femto-cell base station and said CS-dedicated relay device; and second establishing means for acquiring the IP address of said PS-dedicated relay device from said second management device through said first IPsec Tunnel, connecting to said PS-dedicated relay device based on the acquired IP address of said PS-dedicated relay device, and establishing a second IPSec Tunnel between said femto-cell base station and said PS-dedicated relay device, wherein: said femto-cell base station acquires an IP address of said second management device from said CS-dedicated relay device when the first IPsec Tunnel is established between said femto-cell base station and said CS-dedicated relay device, queries said second management device for the IP address of said PS-dedicated relay device through said first IPsec Tunnel based on the acquired IP address of said second management device, and acquires the IP address of said PS-dedicated relay device from said second management device through said first IPsec Tunnel. first establishing means for acquiring the IP address of said CS-dedicated relay device from said first management device, connecting to said CS-dedicated relay device based on the acquired IP address of said CS-dedicated relay device, and establishing a first IPsec Tunnel between said femto-cell base station and said CS-dedicated relay device; and second establishing means for acquiring the IP address of said PS-dedicated relay device from said second management device through said first IPsec Tunnel, connecting to said PS-dedicated relay device based on the acquired IP address of said PS-dedicated relay device, and establishing a second IPSec Tunnel between said femto-cell base station and said PS-dedicated relay device, wherein: said femto-cell base station acquires an IP address of said second management device from said CS-dedicated relay device when the first IPsec Tunnel is established between said femto-cell base station and said CS-dedicated relay device, queries said second management device for the IP address of said PS-dedicated relay device through said first IPsec Tunnel based on the acquired IP address of said second management device, and acquires the IP address of said PS-dedicated relay device from said second management device through said first IPsec Tunnel. said femto-cell base station acquires an IP address of said second management device from said CS-dedicated relay device when the first IPsec Tunnel is established between said femto-cell base station and said CS-dedicated relay device, queries said second management device for the IP address of said PS-dedicated relay device through said first IPsec Tunnel based on the acquired IP address of said second management device, and acquires the IP address of said PS-dedicated relay device from said second management device through said first IPsec Tunnel.