To provide a data transmitting/receiving buffer capable of selecting and observing the waveforms of a transmission signal and reception signal.

This buffer is provided with an AND 5a for calculating the logical product of an output enable signal/OE and reception data RD, and for outputting a reception trigger signal RTG, an inverter 6 for inverting the output enable signal/OE, and an AND 5b for calculating the logical product of the output signal of the inverter 6 and transmission data TD, and for outputting the reception trigger signal RTG. Differential signals D+ and D- at a cable 30 side are observed by an oscilloscope 40 according to the reception trigger signal RTG so that only a reception signal can be observed. Also, the differential signals D+ and D- are observed according to a transmission trigger signal TTG so that only a transmission signal can be observed.