A polarizing optical system comprising: at least, polarizing characteristic imparting means for imparting a polarizing characteristic to light emitted from a light source; analyzer means for converting the polarizing characteristic into light intensity information; and output means for outputting the light intensity information; at least one element constituting the polarizing characteristic imparting means comprising an optical glass having a photoelastic constant C in the range of substantially zero with respect to a wavelength range of 0.4 .mu.m to 3.0 .mu.m. The optical glass has a photoelastic constant C in the range of -0.8 to +0.8 (10.sup.-8 cm.sup.2 /N) with respect to a wavelength range of 0.4 .mu.m to 3.0 .mu.m, and has the following composition when represented in terms of wt.% of oxides:SiO.sub.2 : 17.0-27.0% (35.5-57.0 mol %)Li.sub.2 O+Na.sub.2 O+K.sub.2 O: 0.5-5.0% (0.7-20.0 mol %)PbO: 72.0-75.0% (39.1-45.0 mol %)As.sub.2 O.sub.3 +Sb.sub.2 O.sub.3 : 0-3.0% (0.0-2.0 mol %)The above-mentioned optical glass for polarizing optical system causes substantially no optical path difference based on an optical anisotropy, even when a mechanical external stress or a thermal stress occurs. Accordingly, it is possible to easily attain a polarizing optical system which is capable of well retaining the polarizing characteristic of optical information by substantially obviating the effect of the thermal stress or mechanical external stress.