To provide a flat foil for economically manufacturing a metallic honeycomb body in which a characteristic for making an exhaust gas to a turbulent flow is excellent by forming an uneven row consisting of an unperforated unevenness part on the wave surface between the tops of the flat foil with microcorrugation and also forming an undulated wave.

Firstly, a flat foil is formed into the flat foil with microcorrugation by a microcorrugation formation roller. Then, when the flat foil with microcorrugation is used as a starting material and formed into a metallic honeycomb body by an uneven row formation roller, the uneven row alternately consisting of unperforated unevenness parts 11, 12 is formed on the wave surface of microcorrugation in the direction for passing the exhaust gas. Simultaneously, waveform having desired wave height h2 and pitch p2 is formed on the corrugated foil with microcorrugation in the direction F for passing exhaust gas. In such a way, the flat foil having a special structure which is used for the metallic honeycomb body is manufactured efficiently and economically.