Abstract: For obtaining a central processing unit to perform, with the same operation code, an operation in which a carry input is effective and an operation in which the carry input is invalid or an operation in which a borrow input is effective and an operation in which the borrow input is invalid, between an output of a carry and borrow flag and a carry and borrow input of an ALU there is provided a switching circuit to switch the input of the ALU by a control signal different from a control signal of the central processing unit due to an operation code.