A method and a device or kit for detecting a nucleic acid, which enable simple and precise visual detection of a nucleic acid amplified by an nucleic acid amplification method, without necessity of special devices are provided. The method for detecting a nucleic acid in a sample comprises: contacting a sample with a dye to react with each other; and observing a substance produced by the reaction with visible light, and evaluating the presence or absence of a nucleic acid by eye. The device or kit for detecting a nucleic acid in a sample comprises: a carrier that holds a dye which can bind to a nucleic acid; a path for passing a sample through the carrier; and an evaluation part for observing a substance produced by the reaction between the sample and the dye with visible light, and evaluating the presence or absence of a nucleic acid by eye.