A method for forming a positive image, which comprises exposing an image-forming material comprising a substrate and a positive photosensitive composition layer containing a novolak resin and a photo-thermal conversion material which absorbs light from an image exposure light source and converts it to heat and not containing a thermally decomposable material which decomposes by the action of heat generated by the photo-thermal conversion material upon absorption of light from the image exposure light source, formed on the substrate, followed by development with an alkali developer containing an amphoteric surfactant to form a positive image.