Disclosed is a transmission line loaded dual-band monopole antenna, which realizes operation in dual bands with a single antenna. The dual-band monopole antenna includes a monopole antenna and a transmission line load. The monopole antenna has a signal feeding terminal and a load connection terminal. The load connection terminal is connected to the transmission line load. The transmission line load includes a core transmission line, an outer circumferential conductor, and a short-circuit section. The core transmission line has an antenna connection terminal and a short-circuit terminal. The antenna connection terminal is connected to the load connection terminal of the monopole antenna. The outer circumferential conductor circumferentially surrounds and is spaced from the core transmission line and the outer circumferential conductor has an open terminal and a short-circuit terminal. The opening of the open terminal of the outer circumferential conductor faces the antenna connection terminal of the core transmission line so that the outer circumferential conductor forms an open structure facing the monopole antenna.