A memory system may include a semiconductor memory and a memory controller. The memory controller may include an adjustment circuit configured to receive a first signal having a first duty cycle, and intermittently output a second signal to an outside of the memory controller on the basis of a control signal, the second signal having a second duty cycle which is different from the first duty cycle. The memory controller may further include a selector circuit configured to receive the second signal, receive a third signal which is generated on the basis of the second signal, and output a selected one of the second signal and the third signal. The memory controller may further include a control circuit configured to generate the control signal on the basis of the selected one of the second signal and the third signal output from the selector circuit.