To obtain an optimal throughput when a use situation of a CPU or a network fluctuates.

A file transmission method has: a transmission step of sequentially transmitting a plurality of data comprising a file via a network; a compression step of compressing the respective data transmitted in the transmission step; and a compression determination step of estimating a time for transmission processing required for transmission when compression does not occur on the basis of compression result of the respective data transmitted compressed and compression-transmission information about a transmission result and comparing the estimated time for processing with a total time for processing required for actual compression and transmission to determine whether to continue the compression processing in the compression step. When a first prescribed time passes after the compression processing is stopped by the determination, the compression processing starts, when a compression period until a second prescribed time passes after the compression processing is started or it is determined that compression processing should be continued, determination is made on the basis of compression-transmission information obtained at least during the compression period.

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