The delay locked operation is intermittently conducted only when a command or signal is supplied from outside, and a delay time changed in the delay locked operation is retained thereafter in the period that the command or signal is not supplied. Also, the dummy pattern used in conducting the phase comparison between internal clock ICK and external clock ECK is obtained through the output circuit that has the same characteristics as the output circuit from which data are actually output. Therefore, the accurate coincidence between internal clock ICK and external clock ECK can be obtained regardless of the parasitic inductive and capacitive loads that are influenced depending on the characteristic of package and the mounting conditions. Thereby, the delay locked operation can be always conducted accurately.