An operating method of a server, comprising, mediating a video call session between a first terminal and a second terminal; receiving satisfaction information on the video call session of a user of the first terminal from the first terminal; preparing combination of a specific type of personal information about a user of the first terminal and facial characteristic information about a user of the second terminal; calculating a correlation between the combination and the satisfaction information corresponding to the combination; receiving a video call mediating request from a third terminal and from a plurality of candidate terminals, and predicting satisfaction information of a user of the third terminal with respect to each of the candidate terminals; and choosing a fourth terminal among the candidate terminals.