A wireless signal transmission device is provided. The wireless signal transmission device includes a reflective surface and a receiver. The reflective surface reflects a wireless signal. The receiver receives the wireless signal reflected. The receiver includes a receiver body, a wave guide, a transmission unit and a medium sheet. The wave guide includes an opening end and a connection end connected thereto. The transmission unit is disposed in the wave guide adjacent to the connection end for receiving the wireless signal. The medium sheet is disposed in the wave guide, wherein the medium sheet comprises a first section and a second section, the first section is adjacent to the transmission unit, the second section is adjacent to the opening end, the first section has a first dielectric constant, the second section has a second dielectric constant, and the first dielectric constant is smaller than the second dielectric constant.