An advertisement that has been watched by a friend but has not been watched by a target player is controlled to be displayed at a timing satisfying a timing condition defining a timing at which the advertisement is displayed, in a game played by the target player. At that time, information indicating that the advertisement has been watched by the friend is also controlled to be displayed. A reward for watching the advertisement is given to the target player. The reward changes in accordance with the number of the friends who have watched the advertisement and a friendship level of the friend. The target player is further notified that the advertisement has been watched by the friend, and thus the reward has changed.