1. A method for producing unsaturated aldehydes and unsaturated carboxylic acids corresponding to a raw material in which at least one compound selected from propylene, isobutylene, t-butyl alcohol, and methyl-t-butyl ether is added as the raw material and subjected to gas phase contact oxidation with molecular oxygen or a molecular oxygen-containing gas, using a fixed-bed multistage heat medium circulating type of multi-tubular shell-and-tube reactor filled with a catalyst,wherein the multistage heat medium circulating type of multi-tubular shell-and-tube reactor includes a cylindrical shell, a plurality of tube sheets for separating the inside of the shell into a plurality of independent spaces, a baffle for dividing the plurality of independent spaces inside the shell into two spatially continuous zones, and a plurality of reaction tubes fixed to the inside of the shell while penetrating through the plurality of tube sheets and the baffle,
wherein, in the plurality of independent spaces inside the shell, heat transfer to the reaction tube is performed independently at a temperature of 280 to 400° C. by the flow of an independent heat medium,
wherein at least four spatially continuous fixed catalyst layer zones exist in the reaction tube, the fixed catalyst layer zones have high activity in the direction from an inlet to an outlet of the reaction tube, and the fixed catalyst layer zones include first to fourth fixed catalyst layer zones, and
wherein a length (L) and an outer diameter (D) of the catalyst decreases from the first to the fourth fixed catalyst layer zones.