In late years accidents due to health and the state of the driver increase. For those accident prevention, we developed the steering sensor which could measure the Vital signs of the driver for non-restriction. This sensor measures an electrocardiogram (the first instruction) and the pulse wave of the driver by holding a steering with both hands. Using two indexes, RRI and PTT (pulse wave propagation time) provided from these electrocardiograms and pulse waves, we tried the stress evaluation of the driver this time. First, we gave plural stress (mental workload) to five subjects in a laboratory and evaluated a change of RRI and PTT and confirmed that stress was discriminative. Then, we acquired RRI and PTT in plural driving environment and compared them with the subjectivity evaluation. As a result, we found the possibility that can distinguish plural driver's stress by using the steering sensor which we developed.