A data writing device includes secondary storages, an interface circuit which obtains data, and a computer apparatus which writes the data obtained in one of the secondary storages. The computer apparatus includes writing processes corresponding to the secondary storages as an application, respectively; a monitoring process which detects quantities of data whose writing is finished in the secondary storages; and a data distribution process which selects a secondary storage as a target for next writing based on requested data quantities of the secondary storages and the finished data quantities thereof, and instructs a writing process corresponding to the secondary storage as a target for next writing to write.