This invention relates to a vehicular atmosphere purifying apparatus. An object of this invention is to provide a vehicular atmosphere purifying apparatus that, with a less expensive configuration, is capable of diagnosing deterioration in the performance of an ozone purifier. In a routine shown in Figure 12, when it is determined that there is a deterioration diagnosis request, the amount of moisture that has already accumulated at ozone purification sites of activated charcoal at the time of the request is calculated (step 210). If the accumulated moisture amount is equal to or greater than a predetermined amount, it is determined whether the state is such that calculation of a desorbed moisture amount is possible (step 230). If it is determined that calculation of the desorbed moisture amount is possible, the desorbed moisture amount is calculated (step 240), and the calculated desorbed moisture amount and a deterioration determination value are compared (step 250). If the desorbed moisture amount is less than the deterioration determination value, it is determined that the activated charcoal has deteriorated, and an MIL 62 is lit (step 260).
