The microstrip array antenna includes a dielectric substrate formed with a conductive ground plate at a back surface thereof, and strip conductors formed on a front surface of the dielectric substrate. The strip conductors includes a linear main feeding strip line, and a plurality of array elements connected to the main feeding strip line, the array elements being disposed at least one of both sides of the main feeding strip line at a predetermined interval along a longitudinal direction of the main feeding strip line. Each of the array elements includes a sub-feeding strip line connected to the main feeding strip line, a rectangular radiating antenna element connected to a terminal end of the sub-feeding strip line, and a stub connected to the sub-feeding strip line. The stub is disposed between the main feeding strip line and the radiating antenna element.