Provided is an ink supply device for a printing machine which can accurately supply a quantity of ink necessary for acquiring desired concentration while making the fine adjustment of concentration of ink by an operator unnecessary. A control device 34 of the ink supply device includes: a concentration prediction value calculation means 53 which acquires a concentration prediction value when the concentration becomes stable based on concentration measured values of a predetermined number of printed matters; a graph change value calculation means 54 which acquires a graph change value using the concentration prediction value and a concentration target value; and a control graph value calculation means 55 which acquires a control graph value for controlling a rotational angle based on a preset set graph value and the graph change value.