PURPOSE: To easily separate an original photomask plate from a photomask material to be worked after contact exposure by coating at least one of the surface of the photomask plate at the side of the photomask material and the surface of the photosensitive agent of the photomask material with the 2nd photosensitive agent having a property of releasing gaseous nitrogen by a photosensitive reaction.

CONSTITUTION: A metallic layer 5 is formed on a transparent glass substrate 3 and coated with a photosensitive agent 6. The 2nd photosensitive agent 8 (e.g., "Az Resist ") having a property of releasing gaseous nitrogen by a photosensitive reaction is applied to the layer of the agent 6. A very small amount of gaseous nitrogen is required, and by changing the thickness of the applied 2nd photosensitive agent, the amount of released gaseous nitrogen can be regulated easily. A similar effect is produced by coating the surface of an original photomask plate at the side of the photomask material to be worked or both the surfaces of the photomask plate and the photomask material with the 2nd photosensitive agent.