A controller controls an operation of a semiconductor memory device including a plurality of memory blocks. The controller includes a temperature sensing unit, a period storage unit, and a command generating unit. The temperature sensing unit generates temperature information by sensing a temperature of the semiconductor memory device. The period storage unit updates an output period of a dummy read command that allows the semiconductor memory device to perform a dummy read operation, based on the temperature information. The command generating unit generates the dummy read command, based on the output period.