According to one embodiment, a pattern formation method includes forming a first mask layer including a first and a second concave pattern on a first surface of a substrate. The method can include providing a protection film in the first concave pattern. The method can include providing a self-assembling material in the second concave pattern. The method can include forming a first and a second phase in the second concave pattern by phase-separating the self-assembling material. The method can include removing the protection film together with the first phase to form a second mask layer having the first concave pattern and a third concave pattern. The third concave pattern is provided in the second concave pattern, and has an opening width narrower than an opening width of the second concave pattern. The method can include processing the substrate using the second mask layer as a mask.