A sample detection method that uses a thin-layer chromatography plate having a first separating agent layer and a second separating agent layer adjacent thereto and that detects a component in a sample that exhibits an optical response to ultraviolet light or a coloring agent, the method comprising: a step of developing the sample in the first separating agent layer in a direction along the boundary between the first and second separating agent layers; a step of drying a mobile phase in at least the second separating agent layer; a step of changing the orientation of the thin-layer chromatography plate and developing a spot in the first separating agent layer into the second separating agent layer; and a step of detecting a spot that has migrated into the second separating agent layer by exposure to ultraviolet light or by a color-development treatment with a coloring agent, and when a spot has been developed in a first direction in the first separating agent layer, a ratio of the spot migration distance W2 in a second direction in the first separating agent layer to the spot migration distance W1 in the first direction in the first separating agent layer is not more than ±0.5, and wherein the first separating agent layer is formed by coating a support with a first separating agent for optical isomers, which has the optical response, the first separating agent containing a polysaccharide derivative comprising a polysaccharide and an aromatic ester group, aromatic carbamoyl group, aromatic ether group or carbonyl group substituted for all or a portion of the hydroxyl groups or amino groups in the polysaccharide, the second separating agent layer is formed by a second separating agent, which has an optical response that is different from that of the first separating agent, and the optical response of the component is the same as the optical response of the first separating agent, and wherein an inorganic binder selected from gypsum and an organic binder are used in combination as the binder in both the first and second slurries, the gypsum content in the first slurry, expressed as per 100 mass parts of the first separating agent, is 10 to 20 mass parts and the content of the organic binder in the first slurry, expressed as per 100 mass parts of the first separating agent, is 1 to 3 mass parts, and the gypsum content in the second slurry, expressed as per 100 mass parts of the second separating agent, is 2 to 8 mass parts and the content of the organic binder in the second slurry, expressed as per 100 mass parts of the second separating agent, is 2 to 4 mass parts and the same type of coating solvent is used for the first and second slurries. a step of developing the sample in the first separating agent layer in a direction along the boundary between the first and second separating agent layers; a step of drying a mobile phase in at least the second separating agent layer; a step of changing the orientation of the thin-layer chromatography plate and developing a spot in the first separating agent layer into the second separating agent layer; and a step of detecting a spot that has migrated into the second separating agent layer by exposure to ultraviolet light or by a color-development treatment with a coloring agent, and