A calibration device which is configured for calibrating a memory is provided. The calibration device includes an input terminal, a first pull-up circuit, and a first comparator. The input terminal is coupled to an external resistor. The first pull-up circuit is coupled to the input terminal, and configured to receive a power supply voltage. The first pull-up circuit includes a plurality of first pull-up units. The first pull-up units are coupled to each other in parallel. The first comparator is coupled to the input terminal. The first comparator is configured to receive a proportion voltage which is corresponding to the power supply voltage, and output a first control signal to the first pull-up units, such that a resistance of each of the first pull-up units is equal to a resistance of the external resistor.