To provide a method for forming a polycrystalline diamond film, capable of forming the polycrystalline diamond layer whose surface electric characteristics are nearly equal to those of single crystal diamond, capable of forming the diamond layer having a smooth surface not requiring its chemical polishing and mechanical polishing, and capable of forming the polycrystalline diamond thin and thick films not containing bulk detects.

Plural diamond crystal nucleus-producing sites are formed on a substrate, and diamond layers are formed at the sites to continuously form the diamond layers having {100} surfaces and {111} surfaces. In the growth process, such the first growth parameter that the growth in the vertical direction based on the {100} surface of each nucleus-producing site precedes the growth in the vertical direction based on the {111} surface and such the second growth parameter that the growth of the {100} surface precedes the growth of the {111} surface are successively repeated. The process is repeated until the a diamond layer having a large {100} coplanar angle surface having a desired thickness is obtained.