PURPOSE: To avoid high impedance on the input line of an LSI upon removal of a logic section in the terminal of a personal work station comprising the LSI and the logic section which can be removed using a different power supply having I/O function and memory function.

CONSTITUTION: A DC/DC converter (1) provides a VCC power supply for LSI5 whereas a DC/DC converter (2) provides a VDD power supply for a VDD power supply logic section 6. (VCC<VDD) A voltage level regulation circuit 7 pulls the potential of the LSI5 connected through a bidirectional bus line 101 with the VDD power supply logic section 6 up to a level based on the VDD level through the use of a pull up resistor 71. When the VDD power supply is turned OFF, the potential of the LSI5 is pulled down through the use of a pull down resistor thus avoiding high impedance on the input line to the LSI.