Abstract: With regard to a heat treatment furnace (a solution furnace 1 and an ageing furnace 3), a furnace chamber 15 comprises a furnace body 12 opening downward and a floor body 14 closing the lower opening of the furnace body 12 and rotatably driven, and one or plural stages of mounting shelves 16 on which work pieces 8 are mounted are provided in the furnace chamber 15. Hot-air circulation equipments 20A and 20B circulating hot air in the furnace chamber 15 along the peripheral direction when viewed in plan are provided in the furnace body 12. The mounting shelves 16 are fixed to a prop 17 standingly provided on the floor body 14 and are rotated integrally with the floor body 14.