This antenna apparatus comprises: a base body; a first antenna element that extends in a direction perpendicular to a first surface of the base body and that functions as a monopole antenna; a second antenna element that is provided so as to be adjacent to the first antenna element, extends in the direction perpendicular to the first surface of the base body, and functions as a monopole antenna; a ground layer provided to the base body; a connection wire that is provided to the base body and that connects the first antenna element to the second antenna element; a power supply line that is provided to the base body and that is connected to the connection wire; and a first reflector that faces the first antenna element and the second antenna element and that is provided along a direction in which the first antenna element and the second antenna element are adjacent. The first antenna element and the second antenna element are provided along at least one end surface of first to fourth end surfaces of the base body, overlap with the first reflector in a side view from a direction perpendicular to the at least one end surface, and are located between the at least one end surface and the first reflector in a plan view.