A substrate surface cleaning liquid medium and a cleaning method using the cleaning liquid medium are capable of removing finely particulate contaminants more efficiently than conventional techniques from substrates for devices in the production of semiconductor devices, display devices, etc., which cleaning liquid medium contains the following ingredients (A), (B), (C), and (D), has a pH of 9 or higher, and a content of ingredient (C) of 0.01 to 4% by weight: (A) an ethylene oxide addition type surfactant which has an optionally substituted hydrocarbon group and a polyoxyethylene group in the same molecular structure and in which the ratio of the number of carbon atoms contained in the hydrocarbon group (m) to the number of oxyethylene groups in the polyoxyethylene group (n), m/n, is m/n.ltoreq.1.5, (B) an alkali ingredient, (C) hydrogen peroxide, and (D) water.