A diamond substrate manufacturing method includes a step of forming a band-shaped separation layer with applying a laser beam to a diamond ingot by moving the diamond ingot relative to each other and a focal point of the laser beam in a [110] direction perpendicular to a (110) plane, thereby forming a band-shaped one Form a separation layer, which extends inside the diamond ingot in the [110] direction, a grading step with moving the diamond ingot and the focal point relative to each other in a graduation direction parallel to a (001) plane and perpendicular to the [110] direction , a step of forming a planar separating layer with repeating the step of forming a band-shaped separating layer and the dividing step to thereby form a planar separating layer inside the diamond ingot parallel to the (001) plane, the planar separating layer consisting of a plurality of band-shaped separating layers, the S are arranged side by side in the division direction, is constructed, and a separation step with a separation of a diamond substrate along the planar separation layer from the diamond ingot.
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