PURPOSE: To obtain the subject therapeutic agent containing a cationic surfactant, an amphoteric surfactant and a nonionic surfactant, excellent in efficacy in a short period used in a foot-bath for the lesion with fungi such as trichophytons, etc.

CONSTITUTION: This therapeutic agent for dermatomycosis comprises (A) a cationic surfactant, preferably a quaternary ammonium salt, preferably benzalkonium chloride, (B) an amphoteric surfactant, preferably an aminocarboxylic acid or its salt, preferably a long-chain alkyldi(aminoethyl) glycine or its salt and (C) a nonionic surfactant, preferably an ether type nonionic surfactant, preferably a polyoxyethylene alkyl ether. Furthermore, the therapeutic agent is preferably a liquid formulation. The mixing ratio of the ingredients (A):(B):(C) in this therapeutic agent is preferably 1:(0.5-1.5):(2-6).