PURPOSE: To evaluate a risk accurately by precisely specifying an object to be measured under various working environment.

CONSTITUTION: Relative ratios among the output levels of reflected light from objects to be measured at a time when the objects to be measured are irradiated with light having different wavelength from three semiconductor lasers 1a, 1b, 1c of a light source section 1 and relative ratios among the output levels of reflected light as reference values previously stored at every kind of the objects to be measured in a measured-object characteristic storage section 12 are compared. Consequently, since the kinds of the objects to be measured are discriminated, what are the objects to be measured can be decided accurately. Since risks such as collisions are evaluated from the kind information and distance information up to the objects to be measured, the risks can be evaluated with high accuracy, and a car can be controlled and alarms output properly for collision avoidance.