It is known that L-menthol controls smooth muscle contraction. In order to use L-menthol in practice as a digestive tract contraction inhibiting agent in digestive tract endoscopy, it is required to devise means of giving a formulation in which an L-menthol-containing formulation remains stable and transparent or little cloudy over a long time after the production and which shows little foaming at the administration. In the present invention, an antifoaming agent is further added to a formulation for inhibiting smooth muscle contraction or a peristaltic contraction in a digestive tract containing a L-menthol emulsion having an average particle size of less than 100 nm.Thus, it is possible to obtain a formulation that remains stable over a long time, has a high light transmittance, and produces little foam when filled into a container and sprayed at a target area to inhibit contraction to facilitate observation of the area in endoscopic examination of the digestive tract etc.