A thermometer code generator includes n bit storing stages that are coupled to each other, where n is an integer greater than 1, and the n bit storing stages store a thermometer code, and are adapted to increase the stored thermometer code by 1 in synchronization with a clock signal when an up signal is active, to decrease the stored thermometer code by 1 in synchronization with the clock signal when a down signal is active, and to maintain the stored thermometer code in synchronization with the clock signal when both of the up signal and the down signal are inactive.