With the increased sophistication and complexity of medical care, medical personnel are experiencing higher workloads and increased exhaustion. Especially higher workloads for nurses have dire negative impacts on nurses, patients, and healthcare institutions. Consequently, the traditional healthcare system is now being challenged. Team-based healthcare is emerging as a potential solution to this issue, highlighting the need for assessing workload within nursing teams. In this study, we focused on managing workloads for the nursing teams in the ICU because the nurses there face a higher workload as the team composition changes daily, and nurses are directly involved in numerous treatments. Effective teamwork is crucial in workload management, and communication within the team determines teamwork. This study aims to clarify how communication affects the foundation of teamwork and how teamwork formation further affects the mental workload of the nursing team. Analysis of the simulation experiment indicated a relationship between team development observed through communication and mental workload reduction.