Introduction: The efficacy of antifibrotic agents in idiopathic pulmonary fibrosis (IPF) has been demonstrated and early introduction is recommended, especially in patients with preserved performance status (PS). However, there are still many cases that are untreated and followed up. We aimed to determine the proportion of untreated cases of IPF in the real-world data and to assess which factors are associated with non-intervention. Methods: A prospective observational study using questionnaires was conducted on 518 patients with interstitial lung disease (ILD) and their attending physicians who visited a clinic, general hospital, or tertiary respiratory center between December 2019 and October 2020. Patients responded with subjective symptoms and PS, while physicians responded with diagnosis, treatment, and reasons for treatment choices. Principal component analysis (PCA) was performed using age, gender, BMI, medical facility, specialized tests, and symptom severity. Results: We included 518 patients with ILD, 207 with IPF. Of these, 168 were in good PS (?2), which could be indicative of treatment; 130 (77.4%) were not treated with antifibrotic agents. PCA revealed a trend consistent with antifibrotic agent therapy and distribution of medical facilities, with a treatment intervention rate of 16% in general hospitals and 62% in tertiary respiratory centers. In general hospitals, low severity of symptoms (PS, mMRC, and no use of HOT) was a relevant factor for non-intervention with antifibrotic agents (p<0.001). Conclusions: Differences in antifibrotic treatment rates in IPF have been observed between medical facilities. In general hospitals, treatment rates are low in cases with milder symptoms.