This invention provides carbohydrate absorption inhibitor derived from evening primrose seed which is significantly effective to prevent and cure diabetes mellitus and prevent obesity, and the manufacturing method of the same. Carbohydrate absorption inhibitor in this invention is characterized that the effective component is an alcohol extract of evening primrose seed. The aforementioned evening primrose seed is preferably a defatted evening primrose seed. Extracting solvent of the aforementioned evening primrose seed is preferably ethanol, or preferably a 70 to 85% (v/v) aqueous ethanol. Also, this invention is characterized that the carbohydrate absorption inhibitor is an effective component of polyphenol derived from evening primrose seed. The polyphenol is preferably one or more substances selected from among gallic acid, ellagic acid, catechin, pentagalloylglucose, procyanidin, and proantocyanidin. The manufacturing method of the carbohydrate absorption inhibitor in this invention is characterized to be composed of the following processes A to C. Process A: evening primrose is compressed, oil is separated then the compressed cake is obtained. Process B: The aforementioned compressed cake is defatted in fat-soluble organic solvent, and defatted substance is obtained. Process C: The aforementioned defatted substance is extracted by alcohol, and then this extracted liquid is concentrated or evaporated.