A vehicular dust sensor may include a case having an inner space, a light source module disposed in the inner space of the case, and irradiating an air passage with light, the air passage being provided in the light source module for introduction and pass of air and dust, a condensing lens to collect light, emitted from the light source module and scattered by dust in air in the air passage, a light receiving module receiving the scattered light collected by the condensing lens to output an electric signal corresponding to a dust concentration, and an inner housing disposed in the inner space of the case to form the air passage.