An ink supply device of a printing machine, said ink supply device comprising a plurality of ink transfer rollers, an ink fountain roller which constitutes an ink fountain and a control device, wherein the plurality of ink transfer rollers are divided in the lengthwise direction of the ink fountain roller which constitutes the ink fountain are arranged adjacent to the ink fountain roller, the respective ink transfer rollers are individually changeable over between a transfer position where the ink transfer roller is brought into contact with the ink fountain roller and a non-transfer position where the ink transfer roller is disposed away from the ink fountain roller, and using the control device, based on a graph value set corresponding to a pattern area of a printed matter, ink is transferred by changing over a position of a required ink transfer roller for every transfer timing at predetermined intervals, and a rotational angle of the ink fountain roller from a position where the ink transfer roller is brought into contact with the ink fountain roller to a position where the ink transfer roller is separated from the ink fountain roller is controlled for every ink transfer roller thus controlling a circumferential length of ink transferred to the ink transfer roller from the ink fountain roller, wherein the graph value is a target value of an ink quantity indicating a quantity of ink having predetermined color to be used for every ink transfer roller, each ink transfer roller is provided with a roller position switching device which is able to change over the position of the ink transfer roller, each switching device is controllable by the control device, characterised in that device an ink concentration measurement device is provided for measuring the ink concentration of printed matters, and in that the control device comprises: a concentration prediction value calculation means which acquires a concentration prediction value Y when the concentration of ink becomes stable based on concentration of ink measured values X of a predetermined number of printed matters; a graph change value calculation means which acquires a graph change value Gs using the concentration prediction value Y and a concentration target value K; and a control graph value calculation means which acquires a control graph value Y for controlling the rotational angle of the required ink fountain roller based on a preset set graph value Gb and the graph change value Gs, wherein the control graph value is acquired by a following formula, wherein a concentration prediction value Y at a point of time that the measurement is performed n times is acquired by the following formula, wherein a measurement value at n-th time is Xn, an average value of measurement values of n times is Xa, a standard deviation amounting to n times is σ, a deviation value of a measurement value at n-th time is T, a concentration prediction coefficient is α, a concentration target value is K, a ratio of surplus/shortage of ink is L, a graph change value is Gs, and a graph value correction coefficient is β: Y = Xn + T × Xn − Xa × α, T = 10 × Xn − Xa / σ, σ 2 = X 1 − Xa 2 + X 2 − Xa 2 +...... + Xn − Xa 2 / n, wherein, in the above formulae, the standard deviation σ is acquired by using all measurement values (X 1, X 2). -..., X n) acquired in all measurements performed n times, Y = Xn L = Y − K × 100 / K % Gs = Gb × L × β ÷ 100 % wherein, in the above formulae, a graph value before a change is Gb, and a changed graph value is Ga.