A first arithmetic operator (11) includes a first modular arithmetic coding encoder (11b) for encoding a numeric data transmitted by a command from a central controller (31) into a modular arithmetic code, a first arithmetic operation processor (11a) using the numeric data as modular arithmetic coded as an input operand, for executing an arithmetic operation based on a command from the central controller (13), to provide an output in the form of a modular arithmetic code, and a first modular arithmetic code decoder (11c) for determining presence or absence of a bit error in the numeric data output from the first arithmetic operation processor, correcting the bit error, if detected any, to output a decoded numeric data.