In conjunction with a photomask blank comprising a transparent substrate, a pattern-forming film, and an etch mask film, a set of etching conditions for the pattern-forming film is evaluated by measuring a first etching clear time (C1) taken when the etch mask film is etched under the etching conditions to be applied to the pattern-forming film, measuring a second etching clear time (C2) taken when the pattern-forming film is etched under the etching conditions, and computing a ratio (C1/C2) of the first to second etching clear time.