Time information included in a document file can be efficiently shared by multiple people. A time information communication unit (260) receives time information included as a content of a document file. An ID setting unit (254) then sets a time ID for the time information. A time information storage unit (258) relates and stores the time ID and the time information. Thereafter, the time information communication unit (260) transmits the time ID. A change request communication unit (262) receives time change information for changing the time information related to the time ID. The time information communication unit (260) receives time request information for inquiring for time information. A search unit (256) finds time information from the time information storage unit (258) in response to the time request information. The time information communication unit (260) then transmits the time information thus found to the transmission source of the time request information.