A secondary surveillance radar, comprising: transmitting means (G1, G21, G22, G23, G24) for repeatedly transmitting interrogation signals through beams radiated from an antenna to a plurality of targets having transponders; receiving means (G1, G24, G25) for receiving response signals corresponding with the interrogation signals; and management processing means (G26, G27, G28) for dividing each interrogation repetition cycle of the repeatedly transmitted interrogation signal into an all-call period and a roll call period, wherein during the all call period ATCRBS and mode S transponders are captured in air traffic control radar, and in a roll-call period selective interrogation of a mode S transponder are performed, the management processing means further specifying an azimuth angle range for transmitting interrogations to a plurality of targets characterized in that the management processing means is operable to compare a beam-width of the beams radiated from the antenna with the specified azimuth angle range and, if, on the one hand, the azimuth angle range is narrower than the beam-width, is operable to continue interrogations of mode S transponders at every roll-call period, on the other hand if the specified azimuth angle range is wider than the beam-width the management processing means is operable to thin out the mode S interrogations at every roll-call period with prescribed intervals, wherein the management processing means thins out mode S interrogations by not scheduling an interrogation for a mode S transponder in every roll call such that the number of transmissions to a transponder having a low possibility of responding are reduced. transmitting means (G1, G21, G22, G23, G24) for repeatedly transmitting interrogation signals through beams radiated from an antenna to a plurality of targets having transponders; receiving means (G1, G24, G25) for receiving response signals corresponding with the interrogation signals; and management processing means (G26, G27, G28) for dividing each interrogation repetition cycle of the repeatedly transmitted interrogation signal into an all-call period and a roll call period, wherein during the all call period ATCRBS and mode S transponders are captured in air traffic control radar, and in a roll-call period selective interrogation of a mode S transponder are performed, the management processing means further specifying an azimuth angle range for transmitting interrogations to a plurality of targets characterized in that the management processing means is operable to compare a beam-width of the beams radiated from the antenna with the specified azimuth angle range and, if, on the one hand, the azimuth angle range is narrower than the beam-width, is operable to continue interrogations of mode S transponders at every roll-call period, on the other hand if the specified azimuth angle range is wider than the beam-width the management processing means is operable to thin out the mode S interrogations at every roll-call period with prescribed intervals, wherein the management processing means thins out mode S interrogations by not scheduling an interrogation for a mode S transponder in every roll call such that the number of transmissions to a transponder having a low possibility of responding are reduced.