A
beam scanning plane antenna is formed by stacking, in order, a
system connecting portion, a Rotman lens portion, and a
beam scanning antenna portion. The
system connecting portion is formed by stacking, in order, a fourth grounding conductor, a sixth
dielectric, a connecting substrate and a fifth
dielectric. The Rotman lens portion is formed by stacking, in order, a third grounding conductor, a fourth
dielectric, a Rotman lens substrate and a third dielectric. The
beam scanning antenna portion is formed by stacking, in order, a second grounding conductor, a second dielectric, a power feeding substrate, a first dielectric and a first grounding conductor. A plurality of antenna groups that each include an irradiating element, a power feeding line and a first connecting portion, are formed on the power feeding substrate. The Rotman lens substrate includes a Rotman lens pattern, a second connecting portion and a third connecting portion.