To provide a new synchronous information processing system which lightens the burden on a user by automating the synchronization of shared information and further accurately synchronizes information.

A first device 106 and a second device 107 are connected through a network 108. Each of them is equipped with a shared information storage means 104 which holds the same shared information as the other, a shared information update detecting means 102 which detects shared information stored in a shared information storage means 104 of the first device 106 being updated, an updated information storage means 100 which temporarily stores the updated information, a shared information update means 120 which updates the information into latest shared information, an equipment information storage means 103 which holds an identifier for identifying the second device name or second device that holds the shared information, and an update processing confirming means 122 which confirms that the first device 106 and second device 107 both have completed the update processing.