This study examines how quarterly earnings announcements affect financial analysts' earnings forecast revisions and forecast errors. Since 2000, domestically listed firms have been required to report quarterly earnings. If quarterly earnings announcements provide useful information to investors and financial analysts use quarterly earnings reports in their earnings forecasts, different attributes in analysts' earnings forecasts would be expected around earnings announcements. The results found that the frequency of financial analysts' earnings forecast releases increased sharply immediately after the quarterly earnings report date. The absolute value of earnings forecast revisions released by financial analysts around the quarterly earnings announcement event date was significantly larger than the absolute value of forecast revisions released during non-event periods. Additionally, the forecast accuracy of revisions released after each quarterly event date was higher than that of earnings forecasts reported before the quarterly earnings announcement. However, there was no significant difference in forecast error between analysts' earnings forecasts reported within four days after the quarterly earnings report and those reported after four days. These results indicate that financial analysts use quarterly earnings reports in their earnings forecasts, and that the information effect of financial analysts' earnings forecasts is greatest immediately following the quarterly earnings report.