A communication system comprising a plurality of radio relay stations (110, 210) for relaying a radio communication with a terminal apparatus, wherein each of the plurality of radio relay stations (110, 210) is provided in each of a plurality of High Altitude Platform Stations, HAPSs, (10, 20) controlled so as to be located in a floating airspace with an altitude less than or equal to 100 [km] by an autonomous control or an external control, wherein each of the plurality of radio relay stations (110, 210) forms a three-dimensional cell (41, 42) in a predetermined cell-formation target airspace between each of the HAPSs and a ground level or a sea level, when each of the HAPSs (10, 20) is located in the floating airspace, wherein each of the plurality of radio relay stations (110, 210) forms a beam (100, 200) for performing a radio communication with the terminal apparatus toward the ground level or the sea level, wherein the plurality of beams (100, 200) adjacent to each other in the cell-formation target airspace partially overlap with each other, wherein the plurality of beams (100, 200) is formed so as to cover an overall upper end surface of the cell-formation target airspace, wherein the plurality of HAPSs (10, 20) includes a first HAPS and a second HAPS, and wherein each beam of the radio relay stations (110, 210) of the first HAPS and the second HAPS is formed in a conical shape, characterized in that when a divergence angle of the beam of the radio relay station of the first HAPS is defined as θ1 [rad], a divergence angle of the beam of the radio relay station of the second HAPS is defined as θ2 [rad], an altitude of the radio relay station of the first HAPS is defined as Hrs1 [m], an altitude of the radio relay station of the second HAPS is defined as Hrs2 [m], a horizontal interval between the radio relay station of the first HAPS and the radio relay station of the second HAPS is defined as Drs [m] and an altitude of the upper end of the cell-formation target airspace is defined as Hcu [m], a following expression is satisfied. Hrs1 − Hcu × tan θ 1 + Hrs2 − Hcu × tan θ 2 ≧ Drs wherein each of the plurality of radio relay stations (110, 210) is provided in each of a plurality of High Altitude Platform Stations, HAPSs, (10, 20) controlled so as to be located in a floating airspace with an altitude less than or equal to 100 [km] by an autonomous control or an external control, wherein each of the plurality of radio relay stations (110, 210) forms a three-dimensional cell (41, 42) in a predetermined cell-formation target airspace between each of the HAPSs and a ground level or a sea level, when each of the HAPSs (10, 20) is located in the floating airspace, wherein each of the plurality of radio relay stations (110, 210) forms a beam (100, 200) for performing a radio communication with the terminal apparatus toward the ground level or the sea level, wherein the plurality of beams (100, 200) adjacent to each other in the cell-formation target airspace partially overlap with each other, wherein the plurality of beams (100, 200) is formed so as to cover an overall upper end surface of the cell-formation target airspace, wherein the plurality of HAPSs (10, 20) includes a first HAPS and a second HAPS, and wherein each beam of the radio relay stations (110, 210) of the first HAPS and the second HAPS is formed in a conical shape, characterized in that when a divergence angle of the beam of the radio relay station of the first HAPS is defined as θ1 [rad], a divergence angle of the beam of the radio relay station of the second HAPS is defined as θ2 [rad], an altitude of the radio relay station of the first HAPS is defined as Hrs1 [m], an altitude of the radio relay station of the second HAPS is defined as Hrs2 [m], a horizontal interval between the radio relay station of the first HAPS and the radio relay station of the second HAPS is defined as Drs [m] and an altitude of the upper end of the cell-formation target airspace is defined as Hcu [m], a following expression is satisfied. Hrs1 − Hcu × tan θ 1 + Hrs2 − Hcu × tan θ 2 ≧ Drs