An arithmetic unit includes a multiplier multiplying first and second inputs to output a multiplication result, an adder adding the third input to the multiplication result to output a multiplication addition result, a normalization shift circuit shifting the multiplication addition result left with a left shift amount, and a left shift amount prediction circuit. The adder includes a carry-save adder adding a first addition value and a first carry value to the third input and a full adder outputting the multiplication addition result. The left shift amount prediction circuit includes a leading zero count circuit generating a leading zero count, a leading one count circuit generating a leading one count, and a correction circuit correcting the leading one count to zero when NOR of respective least significant bits of the M upper order bits of the second addition value and the second carry value of the full adder is true.