An expanding apparatus supplies an expanding agent to an impregnating vessel, and continuously supplies and discharges a material, e.g., a tobacco material to and from the impregnating vessel through a valve while pressure-increasing or pressure-decreasing the material, thereby continuously expanding the material. The expanding agent supplied to the impregnating vessel, the valve, and the like is recovered and, air, an impurity gas, or the like mixed in it is removed. Thereafter the expanding agent is pressure-increased to a high pressure and supplied to the impregnating vessel and the valve again.