PURPOSE: To prevent power from being uselessly consumed for an unwanted address signal line by selecting an address signal line, for which a transmitted address bit is matched with a reference address bit, and turning it to high impedance.

CONSTITUTION: Address signal lines 2A (20-27) and 2B (28-215) for accessing a memory are connected to a microprocessor 1, an address signal line selecting circuit 3 for selecting the prescribed address signal lines 2A and 2B is provided inside the microprocessor 1, and a bit information signal line 5 is provided to output the bit information of the selected address signal line. The address signal line selecting circuit 3 can select the prescribed address signal line by designating any address bit while using a register consisting of that circuit. When the prescribed number of address bits are matched with the reference address bit, its coincidence signal is outputted to an external decoder and all the signal lines for transmitting the prescribed number of address bits are turned to the high impedance.