PURPOSE: To enable tests at every functional block by simple circuitry having few addition circuits and wirings by bringing all of outputs from each division circuit to tri-state outputs and connecting input/outputs not connected to primary input/output pins in the input/outputs of the division circuits to the primary input/output pins not connected to the division circuits through tri-state elements.

CONSTITUTION: An external input 101 and an output 106 from a functional block 2 are input to a functional block 1, and the functional block 1 outputs an output 102 and an output 105. An input 103 and the output 105 are input to the functional block 2, and the functional block 2 outputs an output 104 and the output 106. The external output 101 is output to the output 105 through a tri-state element 25 and further to the output 104 through an element 26 from the output 105, and the input 103 is output to the output 106 through an element 28 and further to the output 102 through an element 27 from the output 106. Elements 21∼24 are turned ON on actual operation, the elements 25∼28 are turned OFF, the output 105 is input to the functional block 2, and the output 106 is input to the functional block 1. Accordingly, tests are enabled at every division circuit from the outside while simplifying circuitry.