To provide a method for removing an acidic deposit containing a sulfur compound, whereby the terminal point of the cleaning state can be ascertained simply and efficiently without necessity to visually directly observe the cleaning state or to observe the behavior of the pH value of the cleaning fluid. A method for removing an acidic deposit containing a sulfur compound, which comprises contacting the acidic deposit with a prescribed amount of an aqueous cleaning fluid, characterized in that the concentration of sulfate ion (SO 4 2- ) in the aqueous cleaning fluid is measured, and the contact with the aqueous cleaning fluid is terminated after the increase per hour of the measured value becomes not more than 10%.