A transmission control device that drives multiple antennas having different transmission ranges controls a genuine transmission antenna among the multiple antennas to transmit, with use of a carrier wave, a genuine code for activating a portable device and a noise determination purpose burst signal for determining a noise in the portable device after the transmission of the genuine code, and controls each antenna of a remaining antenna group, which includes remaining antennas except the genuine transmission antenna, to transmit the noise determination purpose burst signal at a transmission time point, which is set different from one another and shifted from a transmission time point of the noise determination purpose burst signal from the genuine transmission antenna. The transmission ranges of the multiple antennas including the genuine transmission antenna are set to not have a common area.