The number of medical-condition-caused car accidents (MCCCAs) in transport industry (bus, truck, and taxi) recently increases. MCCCAs including cerebrovascular and cardiovascular disease lead to loss of consciousness, thus result in injury and loss of life, and heavy compensation payment. Toward this problem, conventional systems detect closing of eyes, and fallen down state as to prevent car collisions. However, the support is taken after driver losing consciousness. To prevent MCCCAs, it is important to find out abnormal signs before driver losing consciousness. It is challenging to detect abnormal signs not only early but also with high confidence level (CL). This paper proposes a novel method that multi-modally monitors driver to detect abnormal signs which can be cues for estimating a driving-disable state in future and performs voice interaction based on the result of monitoring to clarify the internal state of the driver. Considering no data of abnormal signs, this study developed the system using normal data and pseudo abnormal data, and method of outlier detection was used for abnormal signs detection. As results of experiment, we found the relationship between cue signs and CL, and the proposed system can detect `sleepiness' state with accuracy of 80%. Voice interaction system did not increase driver's mental demand.