It is an object of the present invention to play back other content on any timing without being restricted to the embedded timing of watermark data embedded in the content even when the progress time of the content fluctuates. The content playback program in the present invention causes a computer to realize: a first table for associating and storing a synchronization point ID embedded as watermark data with a scheduled timing for the synchronization point based on a synchronization reference timing for the main content; a second table for storing a scheduled start timing for first sub-content based on the synchronization reference timing; a detection function for detecting the synchronization point ID embedded as watermark data from second sub-content played back based on the progress of the main content; an acquisition function for acquiring the scheduled timing for the synchronization point based on the detected synchronization point ID and the first table, and acquiring the difference between the scheduled timing of the acquired synchronization point and the detection timing for the synchronization point ID based on the synchronization reference timing; a determination function for determining a start timing for the first sub-content based on the acquired difference and the second table; and a control function for controlling playback of the first sub-content based on the determined start timing for the first sub-content.