A method for providing information for prediction of responsiveness of a subject to a first-protein-targeting drug, the method comprising the steps of: preparing a substrate having a first protein immobilized thereto by adding a test sample containing the first protein to the substrate; adding and reacting the prepared first protein-immobilized substrate with a marker-conjugated second protein; measuring a signal from the reactant obtained in step; and obtaining a signal value per unit amount of the first protein in the test sample added in step based on the signal measured in step, to measure an activation level, or obtaining a signal value per unit amount of the test sample added in step based on the signal measured in step; and obtaining a signal value per unit amount of the first protein contained in the test sample based on the signal value per unit amount of the test sample obtained in step, to measure an activation level, and further comprising, subsequent to step or, a step of comparing a result obtained in step or with that obtained in a reference sample wherein the reference sample comprises a normal cell or a cell identified for a degree of activation of the signaling pathway in which the first protein is involved, and (a) a step in which, when the activation level of the test sample measured in step or is higher than that measured in the reference sample, the responsiveness to a first-protein-targeting drug in the test sample or a subject from which the test sample is derived is determined to be higher than that in the reference sample; (b) a step in which, when the activation level of the test sample measured in step or is equivalent to that measured in the reference sample, the responsiveness to a first-protein-targeting drug in the test sample or a subject from which the test sample is derived is determined to be equivalent to that in the reference sample; and/or (c) a step in which, when the activation level of the test sample measured in step or is lower than that measured in the reference sample, the responsiveness to a first-protein-targeting drug in the test sample or a subject from which the test sample is derived is determined to be lower than that in the reference sample, wherein the signal value per unit amount of the first protein of step or is a quantitative value of a signal or signal intensity obtained by dividing the signal value measured in step or by weight or concentration of the first protein in the test sample added in step. preparing a substrate having a first protein immobilized thereto by adding a test sample containing the first protein to the substrate; adding and reacting the prepared first protein-immobilized substrate with a marker-conjugated second protein; measuring a signal from the reactant obtained in step; and obtaining a signal value per unit amount of the first protein in the test sample added in step based on the signal measured in step, to measure an activation level, or obtaining a signal value per unit amount of the test sample added in step based on the signal measured in step; and obtaining a signal value per unit amount of the first protein contained in the test sample based on the signal value per unit amount of the test sample obtained in step, to measure an activation level, and further comprising, subsequent to step or, a step of comparing a result obtained in step or with that obtained in a reference sample wherein the reference sample comprises a normal cell or a cell identified for a degree of activation of the signaling pathway in which the first protein is involved, and (a) a step in which, when the activation level of the test sample measured in step or is higher than that measured in the reference sample, the responsiveness to a first-protein-targeting drug in the test sample or a subject from which the test sample is derived is determined to be higher than that in the reference sample; (b) a step in which, when the activation level of the test sample measured in step or is equivalent to that measured in the reference sample, the responsiveness to a first-protein-targeting drug in the test sample or a subject from which the test sample is derived is determined to be equivalent to that in the reference sample; and/or (c) a step in which, when the activation level of the test sample measured in step or is lower than that measured in the reference sample, the responsiveness to a first-protein-targeting drug in the test sample or a subject from which the test sample is derived is determined to be lower than that in the reference sample, wherein the signal value per unit amount of the first protein of step or is a quantitative value of a signal or signal intensity obtained by dividing the signal value measured in step or by weight or concentration of the first protein in the test sample added in step.