In a data transfer device, presence/absence of a prescribed header in the received request message is analyzed, and information indicating the presence/absence of the prescribed header, or information indicating either presence or absence of the prescribed header when the prescribed header is either present or absent as a result of analysis is stored. Then, when a reply message corresponding to the request message is received, the presence/absence of the prescribed header is checked by referring to the stored information, and the reply message is transferred according to a result of checking.