In one embodiment, a pattern forming method includes forming a physical guide that includes a first pattern in a first region and a second pattern in a second region on an underlying film, embedding a polymer material into a concave portion of the physical guide, microphase-separating the polymer material, to form a self-assembly pattern having a first and a second polymer sections, observing the self-assembly pattern in the second region, to determine from an observation result whether or not the self-assembly pattern in the first region has a predetermined shape, and selectively removing the first polymer section in the case of determining that the self-assembly pattern in the first region has the predetermined shape. The second pattern includes a pattern with a larger coverage ratio than the first pattern and a pattern with a smaller coverage ratio than the first pattern.