A product-sum calculation apparatus is provided for cumulatively adding up respective products of first input data and second input data. There is further provided a product-sum calculation unit integrated circuit apparatus including the product-sum calculation apparatus, and a cumulative adder. In the product-sum calculation apparatus, a barrel shifter shifts the first input data by a predetermined number of bits based on the second input data, and an adder adds the shifted data outputted from the barrel shifter and inputted through a first input terminal thereof, and data inputted through a second input terminal thereof. A register temporarily stores data outputted from the adder, outputs a stored data to the adder through the second input terminal of the adder, and outputs the stored data through an output terminal. Further, there is provided a multiplexer for selecting either one of third input data inputted through a first input terminal thereof, and data inputted through a second input terminal thereof. Accordingly, the product-sum calculation apparatus calculates a product of the first input data and the second input data, calculates a sum of a calculated product and the third input data, and outputs a calculated sum from the output terminal.