To restrict degradation in accuracy of distance measurement, resulting from shift of an optical axis, even if strain occurs in a glass to which a stereo camera for measuring the distance of an obstacle, is attached.

A pair of independent cameras 12L and 12R, left and right, are attached to the internal surface of the upper part of a front glass 10. Also, two strain sensors 16 and 18 arranged so as to be different from each other in strain detecting direction is attached to the internal surface of the front glass 10 between the cameras 12L and 12R. A control device 20 refers to a correction map in which strains A and B, detected by the strain sensors 16 and 18, and a correction value are associated with each other, and shifts by the correction value the position from which a partial image of a rectangular area is cut out, for a pair of images picked up by the cameras 12L and 12R. thereby calibrating the shaft of an optical axis to restrict a decrease in the accuracy of distance measurement.