A flattened tube fin manufacturing apparatus includes a press apparatus equipped with a mold apparatus forming cutaway portions into which flattened tubes are inserted to produce metal strips; an inter-row slit apparatus cutting the metal strip, in which the cutaway portions have been formed, into predetermined widths to form a plurality of metal strips of a product width arranged in the width direction; and a cutoff apparatus cutting each metal strip of the product width formed by the inter-row slit apparatus into predetermined lengths. The metal strips of the product width outputted from the inter-row slit apparatus advance into the cutoff apparatus after entering a downwardly sagging state. A support portion that contacts and supports lower surfaces of the metal strips of product width in the downwardly sagging state is also provided.