A pattern forming method includes a step of forming a photosensitive organic material layer by providing, on a substrate, a photosensitive organic material which is protected by a hydrophobic photodegradable group and is capable of generating a hydrophilic group selected from the group consisting of amino group, hydroxyl group, carboxyl group, and sulfo group by light irradiation; a step of selectively exposing the photosensitive organic material layer to light in a pattern to generate the hydrophilic group at an exposed portion; a step of providing a block polymer having a hydrophilic segment and a hydrophobic segment, on the photosensitive organic material layer after the exposure, to separate segments of the block polymer into the hydrophilic segment at a portion where the hydrophilic group generated by the exposure is present and the hydrophobic segment at a portion where the hydrophilic group is not present; and a step of removing one of the separated segments to form a pattern of the other segment.