A liquid supply device includes a pressure unit configured to generate a pressure to supply liquid to a printing unit, the printing unit configured to discharge the liquid and perform printing on a printing medium; a pressure detecting unit configured to detect the pressure generated by the pressure unit; and a control unit configured to drive the pressure unit with a power corresponding to a liquid consuming speed of the printing unit if the pressure detecting unit detects a lower pressure than a predetermined pressure while the printing unit discharges the liquid.