A relative angle detecting system permitting a wider range of detectable angles and offering a small detection error by using polarization and a virtual reality providing system using the same are disclosed. The relative angle detecting system includes a light source having a given polarizing direction and a light reception unit in which a plurality of polarization filters having different polarizing directions other than 90 degree and a plurality of light-receiving devices for receiving light passing through the filters are incorporated, and a relative angle is calculated on the basis of a combination of strengths of output signals of the plurality of light-receiving devices.