A data output buffer for a memory device having a memory chip includes a detection unit for detecting an external output data and outputting a detection data, a clock signal adjusting unit coupled to the detection unit for comparing the detection data from the detection unit and a data outputted from the memory chip in accordance with an externally applied clock signal and outputting a first signal and a second signal, and an output buffer unit coupled to the clock signal adjusting unit and outputting a data in accordance with the first signal and the second signal.