In this paper, we present a robotic system which automatically searches and detects the longitudinal section of the carotid artery using a conventional medical ultrasound diagnostic system. In order to obtain a clear image of the carotid artery ready for medical diagnosis, the authors developed real-time image processing algorithms to detect the carotid artery and tissue layers of its walls in the B-mode ultrasound images. Sequential patterns of the ultrasound probe trajectory for scanning the surface of the neck and searching the carotid, were implemented and tested on the Waseda-Tokyo Women's Medical-Aloka Blood Flow Measurement Robot System No. 1 Refined II (WTA-1RII). An experiment with eleven volunteers was carried out and the results show that the system obtained clear images of the carotid artery in 91% of the trials.