In a data flow machine, a program stored in advance is read out based on a tag included in a packet when the packet including first data is inputted from an external portion. Then, an instruction packet is formed by the content read out as a new tag and the first data, so that the instruction packet is outputted. Second data including the same tag as that included in the first data of the instruction packet read out from the program memory is detected. Firing processing is performed with respect to the first data and the second data as a pair and arithmetic processing is performed according to the instruction as a part of the tag included in an arithmetic packet, so that the arithmetic packet is outputted as a packet. The tag included in the packet is determined and the packet is outputted to an external portion or is inputted again to the internal portion.
