To prevent uneven exposure and blurring of the outline of a formed thin film when a thin film is formed on a glass surface by photolithography.

A method of forming a thin film comprises: a step of forming a light absorbing film 12 which reduces irregular reflection of light on a surface of glass 11; a step of forming a photoresist layer 13 on the light absorbing film 12; a step of performing exposure after putting a photomask 15 in which a prescribed pattern has been drawn on the glass 11 on which the photoresist layer 13 has been formed; a step of removing a part of the photoresist layer 13, by development, formed on the surface of a portion 16 on which a thin film is formed; a step of forming a thin film 14 on the portion from which at least the photoresist layer 13 has been removed in the preceding step; and a step of removing the remaining photoresist layer 13.