PURPOSE: To improve the measurement accuracy of a visual range measuring instrument which does not require any adjustment on its optical axis and can be easily set by preventing the influence of the contamination of the air and a lens system and deterioration of a light source, as well as optical axis misalignment due to an external force.

CONSTITUTION: A light emitting section 7, first light receiving section 8 for transmitted light, and second light receiving section 9 for scattered light are integrally supported in an enclosure 1. When it becomes snowy or foggy 21 at the time of measuring a visual range, the light 20 emitted from the section 7 collides with the snow or fog 21 and transmitted light 22 decreases and the amount of scattered light 23 increases. An arithmetic processing circuit 18 finds the visual range corresponding to the concentration of the snow or fog 21 by performing arithmetic processing on the quantities of transmitted light 22 and scattered light 23. Because of the arithmetic processing, the influence of the contamination of a lens system and deterioration of the light source 10 of the light emitting section 7 can be prevented to some extent.