IEEE 802.11ad is expected to be used as in-vehicle communications for high-speed transmission. Recently, radar systems using frequency modulated continuous wave (FMCW) signals in the 60 GHz band have been investigated for a child presence detection in a vehicle. Therefore, there is a concern that the in-vehicle radio communication system could be interfered with by the radar system. In this paper, transmission experiment of IEEE 802.11ad signals with existence of FMCW signals was conducted in a vehicle since the impact of the mutual interference has not been clarified. The results show that if the transmit antenna and the receive antenna face each other, the stable communication can be established in a vehicle even if the FMCW signal interferes. In addition, stable communications are confirmed by using reflection from the vehicle body as long as received signal power is beyond -33 dBm.