A method of recovering an inert material having a hollow cylindrical shape loaded in a fixed-bed reactor, wherein, in the fixed-bed reactor, the inert material is loaded in an inert material layer provided between a first-stage catalyst layer and a second-stage catalyst layer, the first-stage catalyst layer is loaded with a first-stage catalyst for producing acrolein from propylene, and the second-stage catalyst layer is loaded with a second-stage catalyst for producing acrylic acid from acrolein, the method comprising the steps of: extracting the inert material from the fixed-bed reactor; washing the extracted inert material; and screening the washed inert material, wherein the screening step comprises the steps of: determining quality for screening the inert material, and then separating the inert material, and it is determined in the step of determining quality for screening the inert material whether or not the cross-sectional shape (circular shape) of the inert material satisfies the following criteria: the outer diameter is within ±20% of a reference value before use; matter sticking to the surface and inside of the material, whose thickness is 1.0 mm or more, is not contained; and, if the inert material has a seam, a clearance at a seam is 4 mm or less. wherein, in the fixed-bed reactor, the inert material is loaded in an inert material layer provided between a first-stage catalyst layer and a second-stage catalyst layer, the first-stage catalyst layer is loaded with a first-stage catalyst for producing acrolein from propylene, and the second-stage catalyst layer is loaded with a second-stage catalyst for producing acrylic acid from acrolein, the method comprising the steps of: extracting the inert material from the fixed-bed reactor; washing the extracted inert material; and screening the washed inert material, wherein the screening step comprises the steps of: determining quality for screening the inert material, and then separating the inert material, and it is determined in the step of determining quality for screening the inert material whether or not the cross-sectional shape (circular shape) of the inert material satisfies the following criteria: the outer diameter is within ±20% of a reference value before use; matter sticking to the surface and inside of the material, whose thickness is 1.0 mm or more, is not contained; and, if the inert material has a seam, a clearance at a seam is 4 mm or less. extracting the inert material from the fixed-bed reactor; washing the extracted inert material; and screening the washed inert material, wherein the screening step comprises the steps of: determining quality for screening the inert material, and then separating the inert material, and it is determined in the step of determining quality for screening the inert material whether or not the cross-sectional shape (circular shape) of the inert material satisfies the following criteria: the outer diameter is within ±20% of a reference value before use; matter sticking to the surface and inside of the material, whose thickness is 1.0 mm or more, is not contained; and, if the inert material has a seam, a clearance at a seam is 4 mm or less. determining quality for screening the inert material, and then separating the inert material, and it is determined in the step of determining quality for screening the inert material whether or not the cross-sectional shape (circular shape) of the inert material satisfies the following criteria: the outer diameter is within ±20% of a reference value before use; matter sticking to the surface and inside of the material, whose thickness is 1.0 mm or more, is not contained; and, if the inert material has a seam, a clearance at a seam is 4 mm or less. the outer diameter is within ±20% of a reference value before use; matter sticking to the surface and inside of the material, whose thickness is 1.0 mm or more, is not contained; and, if the inert material has a seam, a clearance at a seam is 4 mm or less.