A substrate for a magnetic disk includes a substrate main body and a film. The substrate main body has two opposing main surfaces and an outer circumferential edge surface, and the outer circumferential edge surface includes a side wall surface, which is orthogonal to the main surfaces, and chamfered surfaces, which are disposed between the main surfaces and the side wall surface. The substrate main body is a glass substrate main body or an aluminum alloy substrate main body, and has a disk shape. The film is an alloy film containing Ni and P, and is provided on a surface of the substrate main body such that the film is formed continuously over the main surfaces, the chamfered surfaces, and the side wall surface of the substrate main body.