Which fundraising strategy is more effective and how donation behavior changes with different monetary amounts are still open questions. This study compares the effectiveness of two fundraising strategies—suggested donation and social information—and examines how different monetary amounts affect donation behavior. We implemented a field experiment on voluntary donations among visitors to a national park. Both fundraising strategies affect donation behavior. However, the donation pattern differs significantly depending on the monetary amounts shown. Our findings provide important insights for designing fundraising campaigns and show how suggested donation and social information affect economic behavior.