A driver condition assessment device is provided which assesses a driver condition of a host vehicle. The device assesses whether a predetermined driving operation is performed, and includes detecting a travelling condition of the host vehicle and detecting a size of a preceding vehicle present ahead of the host vehicle. The device assesses whether a consciousness of a driver of the host vehicle is degraded when a detected travelling condition exceeds a predetermined threshold value and sets the predetermined threshold value depending on the detected size of the preceding vehicle.