Provided are providing an ECG unit which is formed of content information and related information related thereto, and is linked to another ECG unit through the related information, calculating an association-degree score between the pieces of content information based on a degree of association of an attribute between the pieces of content information, collecting a history of operation performed for making a transition from a link-source-ECG unit to a link-destination-ECG unit, as a usage log of the ECG unit, calculating a transition score between the ECG units in a manner that a weight of a larger correction coefficient is assigned to a number of usage logs, as there are more attributes of content information having low degree of association with each other between the link-source-ECG unit and the link-destination-ECG unit, and generating an ECG unit linked to another ECG unit, based on the association-degree score and the transition score.