A user who is responsible for the entire operation of kintone.com.
This administrator configures common settings used in kintone.com, such as adding users and configuring security settings.
Adding Users to the Kintone Users & System Administrators

A user who is responsible for the operation of Kintone. This administrator configures the features and access permissions of Kintone.
Kintone Users & System Administrator is automatically set as the system administrator.
You can increase the number of system administrators only, separately from Kintone Users & System Administrators.
Kintone Help: System Administrator

A special user who is registered by the system automatically when you start using kintone.com.
Administrator is used for specific functions. For this reason, it cannot be used as a user.
What Is the Administrator Account?

A user who manages users and departments in a certain department.
For example, you can put the Sales Department Manager in charge of managing the child departments and the Sales Division members.
What Is a Department Administrator?