Abstract: In a parallel computer, there are provided a plurality of processor elements 1-1 to 1-n) connected to each other by a network (2); each of said processor elements including a local memory (6) for holding a program and data related thereto, a processor (3) for performing an instruction in said program, a circuit (5) for transferring the data to the other processor elements, and a circuit (4) for receiving the data sent from the other processor element; a memory area (92:8) constructed of a plurality of reception data areas for temporarily storing data received by said receiving circuit, and a memory (92,8) constructed of a plurality of tag areas, provided for each of the reception data areas, for storing a valid data tag or an invalid data tag indicating that the data in the corresponding reception data area is valid or invalid; a transmitting circuit (5) for transmitting the data to be transmitted with attaching a data identifier predetermined by said data; a receiving circuit for writing the data into one of