A low-frequency induction heater includes a primary side coil having a core and a secondary side conductive hollow cylindrical member surrounding the primary side coil. An improvement to the Joule heat generation efficiency and a solution to problems peculiar to composite materials, such as thermal deformation, electrolytic corrosion, and difficulty is sought of manufacture by forming the conductive hollow cylindrical member of a sole stainless steel material of a thickness ranging from 2 mm to 6 mm. In a preferred embodiment, a coil 2 is wound around a rod-like core 1, which is in turn surrounded by a conductive hollow cylindrical member 3 made of a sole stainless steel material of a thickness ranging from 2 mm to 6 mm. When an AC current passes through the coil 2, an alternating magnetic field is set up in the axial direction of the coil 2, which causes an inducted current in the conductive hollow cylindrical member 3. Joule heat is thus generated in the member 3 due to the electric resistance thereof.