of the operation mode transfer system in accordance with the present invention in which corresponding portions to those of fig1 are designated by the same reference numerals and the description thereof is omitted here in fig3 the reference numeral 26 designates a gate second switching circuit consisting of an n channel mos transistor having its first end connected to the second end of the pullup resistor 21 and its second end connected to the ground the gate 26 is brought into a nonconducting state when the l level signal is stored in the register 19 and into a conducting state when the h level signal is stored thereinto since the operation other than the gate 26 is the same as that of the embodiment 1 only the operation associated with the gate 26 will be described since the l level signal is stored in the register 19 when the device 11 is actually operative the gate 26 is brought into the nonconducting state and the potential v m of the signal line d is pulled up thereby exceeding the set value v th1 as in the embodiment 1 on the other hand since the h level signal is stored in the register 19 when the device 11 is inoperative the gate 26 conducts and the pullup resistor 21 is connected to the ground thus the present embodiment 2 forcefully places the potential v m of the signal line d to zero volt which differs from the embodiment 1 that simply disconnects the pullup resistor 21 from the pullup power supply 20 this offers an advantage that the host computer 13 can identify the inoperative mode of the device 11 earlier than in the embodiment 1 in which the potential v m of the signal line d gradually.