A command processing circuit of a memory device includes a clock divider, a clock controller and a command decoder. The clock divider generates a plurality of divided clock signals based on an external clock signal having a first frequency. The divided clock signals have a second frequency lower than the first frequency. Each of the divided clock signals has a phase that is different from phases of the other divided clock signals. The clock controller generates an operating clock signal based on a command signal and the divided clock signals, where the command signal is transferred in synchronization with the external clock signal. The operating clock signal has the second frequency and a phase corresponding to reception timing of the command signal. The command decoder decodes the command signal in synchronization with the operating clock signal.