To provide a heating furnace for adequately inhibiting the partial temperature difference of a workpiece without complicating a structure of the furnace and its control method.

In this heating furnace for heating the workpiece W while conveying the same by a conveying device 2 in the furnace, side heaters 4 are mounted at both sides of the conveyed workpiece W along the conveying direction. Sheathed heaters are used as the side heaters 4, their heat generating parts are position at a preheating temperature rising area and a main heating temperature rising area to adequately inhibit the partial temperature difference of the workpiece.