To provide a monopole antenna having the directivity of wide angle by folding a ground conductor plate at a prescribed angle oppositely to a radiating element.

A monopole antenna 1 is composed of a radiating element 10 and a ground plate 2. The radiating element 10 performs the transmission (reception) of electromagnetic waves and is formed from a wire-shaped or rod- shaped conductor, for example. The radiating element 10 is electrically connected through a coaxial connector 4 to an inner conductor 5a as the central conductor of a coaxial cable 5 at a feeding point 3. The ground plate 2 is folded just at an angle α oppositely to the side of the radiating element 10. Then, it is connected through the coaxial connector 4 to the outer conductor of the coaxial cable 5. The folding angle α of the ground plate 2 is settled within the range of about 30° to 90°. When the monopole antenna 1 is made into antenna for transmission/reception of wireless camera device, even when the position or direction thereof is changed, the electromagnetic waves can be transmitted (received) at almost the fixed level.