PURPOSE: To attain an arithmetic operation by hexadecimal number and decimal numeral, mutual conversion, and arithmetic operation of a trigonometric function or the like by connecting a keyboard interface part with a keyboard, connecting a computer interface part with a computer, and switching an electric calculator mode to a normal mode by a changeover switch.

CONSTITUTION: This adaptor is equipped with a keyboard interface part 21 for connecting a keyboard 18 to an adaptor 19 for the keyboard, a computer interface part 22 for connecting the adaptor 19 for the keyboard to a computer 20, and a changeover switch 23. When the changeover switch 23 is the normal mode, the keyboard interface part 21 is directly connected with the computer interface part 22, and a code signal is transmitted from the keyboard 18 to the computer 20. When the changeover switch 23 is the electric calculator mode, the code signal is transferred from the keyboard interface part 21 to an arithmetic part 24, and the arithmetic result is transferred to the computer interface part 22 at the time of pressing a transfer switch.