The shape and number of surface defects are controlled so that the occurrence of failure is suppressed in an HDD device in which a magnetic head with a very small flying height, such as a DFH head, is mounted.A magnetic disk substrate is characterized in that when laser light with a wavelength of 405 nm and a laser power of 25 mW is irradiated with a spot size of 5 μm and scattered light from the substrate is detected, the number of defects detected to have a size of 0.1 μm to not more than 0.3 μm is less than 50 per 24 cm2 and, with respect to the defects, there is no defect in which, in a bearing curve obtained by a bearing curve plot method using an atomic force microscope, a portion from an apex of the defect to 45% thereof is located in an area of defect height higher than a virtual line connecting from the apex of the defect to 45% thereof.