A data input apparatus includes: a phase detector comparing a phase of a data strobe signal with a phase of a clock signal to output a first phase comparison signal and a second phase comparison signal. A first delay controller determines whether a first data input strobe signal is delayed to output the determined signal as a second data input strobe signal in response to the first phase comparison signal. An internal clock synchronizer synchronizes first aligned data and second aligned data with the clock signal in response to the second data input strobe signal, to output the synchronized first and second data as first internal output data and second internal output data, respectively. A second delay controller determines whether the first internal output data and the second internal output data is delayed in response to the second phase comparison signal, to output the first internal output data and the second internal output data as first output data and second output data, respectively.