According to an embodiment, a data sharing device includes a first storage to store first information; a second storage to store second information that is a copy of the first information; a difference generator to compare, when the first information stored in the first storage is changed, the changed first information with the second information, extract a difference therebetween if any, and generate first difference information indicating the difference; a difference transmitter to transmit the first difference information to another data sharing device; a difference receiver to receive second difference information generated in another data sharing device; a difference reflector to reflect a difference indicated by the second difference information in the first information stored in the first storage, and cause the first difference generator not to generate the first difference information when the difference indicated by the second difference information is reflected.