A parallel computing system includes: each computing node including: a first channel receiving data which a preceding node transfers, and transferring received data to a subsequent node; a second channel receiving data which a preceding node transfers, and transferring received data to a subsequent node; and a computational processor receiving data which the first or second channel has received, and transferring processed data to a subsequent node; an input-output node including: a third channel receiving data which the first channel or the computational processor of a preceding node transfers; a fourth channel receiving data which the first channel or the computational processor of a preceding computing node transfers, and transferring the received data to the second channel of a subsequent computing node; and an input-output processor receiving data which the third channel has received, and transferring inputted and outputted data to the first channel of a subsequent computing node.