A process for reducing a radioactive material of an object containing the radioactive material to a safe level in a living environment, characterized by comprising: the object being at least one selected from the group consisting of an organism, a sewage sludge, a soil and an incineration ash, a heating/pressurizing/pressure release step selected from the group consisting of a step of carrying out a heating process on the object in a state where temperature is less than or equal to the critical temperature of water, water-soluble liquid, or a mixture of water and water-soluble liquid (Hereinafter, "water, water-soluble liquid, or mixture of water and water-soluble liquid" is referred to as "aqueous liquid") and pressure is greater than or equal to the saturated vapor pressure of the aqueous liquid when the object is being immersed in the aqueous liquid to such a degree that the object is covered or to a greater degree and then releasing the pressure, a step of placing the object under pressure and suddenly releasing the pressure when the object is being immersed in the aqueous liquid to such a degree that the object is covered or to a greater degree, and a step of carrying out a heating process on the aqueous liquid and the object in a state where temperature is less than or equal to the critical temperature of the aqueous liquid and the pressure is greater than or equal to the saturated vapor pressure of the aqueous liquid when the object is being immersed in the aqueous liquid to such a degree that the object is covered or to a greater degree and then suddenly releasing the pressure; and a separation step of separating, after the heating/pressurizing/pressure release step, the mixture of the object and the aqueous liquid into liquid and solid. the object being at least one selected from the group consisting of an organism, a sewage sludge, a soil and an incineration ash, a heating/pressurizing/pressure release step selected from the group consisting of a step of carrying out a heating process on the object in a state where temperature is less than or equal to the critical temperature of water, water-soluble liquid, or a mixture of water and water-soluble liquid (Hereinafter, "water, water-soluble liquid, or mixture of water and water-soluble liquid" is referred to as "aqueous liquid") and pressure is greater than or equal to the saturated vapor pressure of the aqueous liquid when the object is being immersed in the aqueous liquid to such a degree that the object is covered or to a greater degree and then releasing the pressure, a step of placing the object under pressure and suddenly releasing the pressure when the object is being immersed in the aqueous liquid to such a degree that the object is covered or to a greater degree, and a step of carrying out a heating process on the aqueous liquid and the object in a state where temperature is less than or equal to the critical temperature of the aqueous liquid and the pressure is greater than or equal to the saturated vapor pressure of the aqueous liquid when the object is being immersed in the aqueous liquid to such a degree that the object is covered or to a greater degree and then suddenly releasing the pressure; and a separation step of separating, after the heating/pressurizing/pressure release step, the mixture of the object and the aqueous liquid into liquid and solid.