PURPOSE: To eliminate the need for a scanning element to scan an antenna beam over an angle the same as a beam scanning angle by changing a tilt angle between a main longitudinal axis and a sub reflection mirror longitudinal axis so as to rotate a sub reflecting mirror around a rotating point with respect to the main longitudinal angle. CONSTITUTION: This system is provided with an antenna feeding section 16 for outputting an electromagnetic radiation ray and with an antenna sub reflection mirror 12 in crossing with a sub reflection mirror longitudinal axis Ls at a rotating point close to an apex 20 and leading an outputted electromagnetic radiation ray. Also, there is provided with an antenna main reflecting mirror 14 having a main longitudinal axis Lm to project the electromagnetic radiant ray from the reflecting mirror 12 as an antenna beam. Further, a drive mechanism 22 that changes a tilt angle between the main longitudinal axis Lm and the sub reflecting mirror longitudinal axis Ls to rotate the reflecting mirror 12 around the rotating point for scanning the antenna beam with respect to the main longitudinal axis Lm is provided. In this system 10, the reflecting mirror 12 is rotated around the apex 20 or the rotating point on the axis Ls in the vicinity to execute beam scanning in a plane. Thus, the scanning antenna beam is projected at a selected scanning angle without moving a feeding section 16 from a fixed position on the axis Lm.