PURPOSE: To enable safe driving for a driver by quantitatively measuring burden in the respective parts of a body to vibration, inputting respective measured values to a fuzzy inference means, calculating the degree of fatigue for the driver by fuzzy inference and notifying the fatigue to the driver.

CONSTITUTION: Respective first and second measuring parts 1 and 3 quantitatively measure the burden in the belly and head to the vibration. When these measured values are supplied as electric signals S1 and S2 to sample-hold circuits 2 and 4, the said circuits 2 and 4 executes sample-hold to these electric signals and supplies hold values as inputs x1 and x2 to a fuzzy inference part 5. The fuzzy inference part 5 executes the fuzzy inference according to plural fuzzy rules stored in a rule storing part 6 and as an inferred result, an output y' (determined value) showing the degree of the fatigue for the driver is supplied through an amplifier 7 to an output device 8. When the output y' reaches a prescribed value, the output device 8 notifies the state of the fatigue to the driver by turning-on a display lamp or operating a warning buzzer.