Disclosed are a method and an apparatus for identifying audio equipment plugs to be connected to a jack interface of an IT terminal including a common jack interface for a headphone, an earphone microphone and a stereo microphone and for automatically providing appropriate setup. An audio CODEC 50 is connected by way of an input/output selector circuit 42 to a jack interface 10 to which an audio equipment plug 70 is to be connected. Also connected to the LEFT and RIGHT signal terminals of the jack interface 10 is an R-V conversion circuit 20. The output voltages V-LEFT 201 and V-RIGHT 202 from the R-V conversion circuit 20 are compared with a reference voltage by comparator circuits 31, 32 for controlling controllers 41, 51 of an input/output selector circuit 42 and an audio CODEC 50 by the comparison outputs.