In a heating furnace 10 where elongate workpieces fed into the heating furnace are sequentially transferred on fixed beams by walking beams from an inlet area to an outlet area, concaves to retain the workpieces are formed at least on the walking beams. A concave in the inlet area for heating the workpieces is increased in width in a transfer direction, while a concave in the outlet area where the heated workpieces are wholly heated to a uniform temperature and retained in position is formed in a corrugated configuration. Despite curving of an elongate workpiece being heat treated as transferred by walking beams in a direction crossing a longitudinal direction of the workpiece, this ensures that the curved workpiece is properly transferred and adequately corrected for the curving.