A synthetic aperture radar to provide high resolution in the azimuth direction under the predetermined conditions of wide observation swathwidth in the range direction, stripmap observation and free PRF (Pulse Repetition Frequency) comprises a transmission antenna 102 for a single system and receiving antennae 104a, 104b for two systems. The beam width in the azimuth direction of a transmission beam 103 from the transmission antenna 102 is set equal to twice as wide as the beam width of each of the receiving antennae 104a, 104b. Moreover, a receiving antenna beam 105a is directed to the moving direction, while the other receiving antenna beam 105b is directed to opposite to the moving direction. The transmission antenna 102 and the receiving antennae 104a, 104b for two systems are used in common by dividing a single array antenna in the elevation direction to configure the receiving antennae 104a, 104b. The antenna size of the transmission antenna 102 in the azimuth direction is set to one half of the antenna size of the receiving antennae 104a, 104b by phase setting of each element of the array antenna or by electrical means when transmitting.