Objective: The objective of this study was to evaluate the effects of earlier intervention by an antimicrobial stewardship team (AST) on antimicrobial use, antimicrobial resistance rates, and the clinical outcomes, without changing the weekly intervention schedule. Methods: A retrospective study was conducted at Fukuoka University Hospital between April 2013 and March 2016. The effects were compared among three study periods (SP): SP1 (patients receiving antimethicillin-resistant Staphylococcus aureus agents and carbapenems for 14 days), SP2 (patients receiving specific antimicrobials for 14 days), and SP3 (patients receiving specific antimicrobials regardless of the duration of treatment). Results: The timing of AST intervention was shortened from an average of 15.5 days after administration in SP1 to 4.2 days in SP3. The antimicrobial use density (AUD) of carbapenems and piperacillin-tazobactam decreased significantly (SP2 vs. SP3, p < 0.05), and the costs of specific antimicrobials decreased (SP1, US$ 1 080 000; SP2, US$ 944 000; SP3, US$ 763 000). The rates of carbapenem resistance among Pseudomonas aeruginosa isolates showed a significant reduction from 16.2% in SP2 to 8.7% in SP3 (p < 0.05). The mortality rate and length of stay did not change during the study period. Conclusions: Earlier intervention by an AST could contribute to the proper use of antimicrobials without adversely affecting patient outcomes.