A pattern forming method is disclosed which comprises providing a to-be-processed film on a substrate, providing a resist film on the to-be-processed film, patterning the resist film, providing a film of a radiosensitive compound on the to-be-processed film such that the patterned resist film is covered with the film of the radiosensitive compound, subjecting the film of the radiosensitive compound to irradiation and a development process, thus exposing an upper surface of the resist film and patterning the film of the radiosensitive compound, and removing the resist film and processing the to-be-processed film, using the patterned film of the radiosensitive compound as a mask.