A semiconductor memory device includes a first buffering unit configured to buffer a first clock for an address signal and a command to be input in synchronization with the first clock, a second buffering unit configured to buffer a second clock for a data signal to be in synchronization with the second clock to output a buffered second clock having the same frequency as the first clock, a data output circuit configured to output an internal data in response to the buffered second clock, a delay unit configured to delay the buffered second clock by a predetermined time, and a phase detector configured to detect a phase difference of an output clock of the delay unit and the output clock of the first buffering unit, and to output the detection result.