This product is obtained in the following method of preparation: Extract the root bark of Paeonia suffruticosa Andrews (Paeonia moutan Sims) (Paeoniaceae) with ethanol solution, then remove the solvent, and dissolve the residue in a 1,3-butylene glycol and water. It contains not less than 0.01w/v% and not more than 0.14w/v% of paeonol.