PURPOSE: To utilize an existing wiring and to execute tests by providing the titled device with a function block selecting circuit for allowing a connection gate to connect a function block independently to a bus line and controlling the connection of the connection gate based on a function block selecting signal.

CONSTITUTION: All outputs E1WE4 of the function block selecting circuit are set up so as to output '0' by usually turning a test mode signal TM to '0' and all transmission gates 6 are interrupted. In case of testing a function block 1c independently by setting up data from the external, the circuit 5 turns the test mode signal TM to '1' and sets up function block selecting signals SB1, SB2 so that only the output E3 is '1'. Since an I/O line of the function block 1c is connected to port circuits 2a, 2b, the block 1c can be independently tested through the circuits 2a, 2b.