A urine detection device is disposed to a urine receiving surface of a toilet stool in which urine, diluting water and reagent are mixed by vertically moving a piston in the cylinder of the detection device, the reaction between them is detected by an electrode and the ingredient in urine is detected. Liquid in the cylinder is stirred by a stirring device to blown air into the reagent reservoir, by which oxygen is dissolved in the reagent. Cleaning liquid is sprayed from the nozzle to the electrode for flushing. An opening is disposed to a supporting wall of the toilet stool, through which the cylinder is detached or attached. The electrode is disposed such that its rear end is directed to the opening and detached or attached through the opening.