A method for flattening a glass substrate includes the steps of preparing plural kinds of etching liquids different from one another in an etching rate, preparing the glass substrate, and etching the glass substrate at least one time with each of the etching liquids and executing the etching a plurality of times in total. When the etchings are executed the plurality of times, an etching rate of the glass substrate with one etching liquid used for one etching of plural etchings is slower than that of the glass substrate with the another etching liquid used for another etching executed after the one etching process of the plural etching processes.