Composite material sheets containing conductive fibers are laminated, and release films are interposed between the sheets so as to extend from one end to the center of the sheets. The sheets are heated under pressure to shape a composite material. Discrete conductive wires through which a measurement current is passed are connected to end surfaces of the respective layers in the composite material on the side on which the release films are interposed. A common conductive wire through which the measurement current is passed is connected to a surface of one of an uppermost layer and a lowermost layer at an end of the composite material opposite to the side on which the release films are interposed. A current is passed between the common conductive wire and the discrete conductive wires. Currents in the respective layers are sequentially or simultaneously measured using an ammeter.