An object of the invention is to speed up processing of adding floating-point numbers. A floating-point adder includes: a first register configured to store a first fixed-point number having a predetermined number of digits corresponding to a result of accumulation of a plurality of floating-point numbers; a first conversion unit configured to convert an input first floating-point number into a second fixed-point number having the predetermined number of digits; a second register configured to store the second fixed-point number; an adder configured to add the second fixed-point number stored in the second register and the first fixed-point number stored in the first register, and store a result of the addition in the first register as the first fixed-point number; and a second conversion unit configured to convert the first fixed-point number into a second floating-point number, and output the second floating-point number.