PURPOSE: To separate respective logical circuits from a full-logical circuit, and to improve the resolution of a fault by providing a two-way element with a returning function to every external signal terminal, and allowing the elements to function in returning mode for a test of the assembly of the logical circuits.

CONSTITUTION: On one substrate of a package wherein a logical scanning circuit for logical circuits 40 and 41, etc., is incorporated, two-way communication type system terminals 91W94, one-way communication type system terminals 90 and 95, a shift input terminal 96, a shift output terminal 97, etc., are provided. A 4-bit number supplied externally to the terminals 91W94 is accumulated by an accumulator 10 through two-way elements 21W24, and the accumulation result is sent out to the terminals 91W94 through register circuits 34W37. A starting signal is supplied externally from the terminal 90 to the accumulator 10, and a carry signal from the accumulator 10 is sent out from the terminal 95. During a test of the assembly of the logical circuits, the two-way elements 21W24 are used as returning-mode function elements by an external signal to separate each logical circuit from a full-logical circuit.