An emulsion comprising L-Menthol, a fat or oil and a surfactant wherein oil particles have an average diameter of 100 nm or less inhibits a content reduction attributed to, for example, evaporation of L-menthol, enhances a light transmission through liquid and is stable despite long-term storage. Thus, the emulsion can be appropriately used in the temporary inhibition of contraction of gastrointestinal tract for, for example, observation of gastrointestinal tract by an endoscope. This emulsion can be obtained by heating an oil-in-water type emulsion comprising L-menthol, a fat or oil and a surfactant at 60° C. or higher.