A floating-point arithmetic device, including a significand output circuit for calculating a difference between exponents, outputting a first significand with a larger exponent, and shifting the remaining significand by the calculated exponent difference, a first bit inverter, an adder, a leading-zero anticipation circuit for anticipating the consecutiveness of leading zeros from the significands, a leading-zero counter for counting the anticipated number of leading zeros, a left shifter for shifting an output value from the adder, a second bit inverter for taking two's complement of an output value from the left shifter, an incrementer for incrementing an output value from the second bit inverter by one, a compensation shifter for shifting an output value from the incrementer, an exponent subtracter for subtracting the number counted by the leading-zero counter from the larger exponent, and a decrementer for decrementing an output exponent from the exponent subtracter by one.