In a multilayer substrate (2), eight front-side antenna portions (8) and eight back-side antenna portions (16) are disposed. Front-side radiation elements (9) in the front-side antenna portions (8) and back-side radiation elements (17) in the back-side antenna portions (16) are arranged in a staggered pattern when being vertically projected onto an back side (2B) of the multilayer substrate (2). The front-side radiation elements (9) are disposed on a front side (2A) of the multilayer substrate (2), and a front-side ground layer (10) is formed near the back side (2B) of the multilayer substrate (2). On the other hand, the back-side radiation elements (17) are disposed on the back side (2B) of the multilayer substrate (2), and a back-side ground layer (18) is formed near the front side (2A) of the multilayer substrate (2). The front-side radiation element (9) and the back-side radiation element (17) are disposed so as not to overlap each other when being vertically projected onto the back side (2B) of the multilayer substrate (2).