Abstract: An antenna device includes: a circuit board; an antenna placed on the circuit board; and a reflector that is erected on the circuit board and extends along its surface. The reflector has: a convexly curved portion protruding toward the antenna, the convexly curved portion reflecting radio waves emitted by the antenna; and a first plane portion and second plane portion that extend from both sides of the convexly curved portion along the surface of the circuit board, form a V shape together with the convexly curved portion in plan view, and reflect radio waves emitted by the antenna. The surface of the convexly curved portion has a shape equivalent to a portion on the outer circumferential surface of a cylinder, the portion being the range of an azimuth angle with respect to a cylindrical axis. The convexly curved portion is inclined toward the antenna with respect to the circuit board.