To provide a method for cutting a Cu-Ga alloy in which even a Cu-Ga alloy ingot with a relatively large Ga composition ratio can be cut into a desired shape without lowering productivity and without causing cracking or chipping.

The method for cutting the Cu-Ga alloy includes a heat treatment step and a slicing step. In the heat treatment step, the Cu-Ga alloy ingot 81 with a rectangular parallelepiped shape manufactured by melt casting is heat-treated under a temperature not less than 450°C but less than 700°C. Next, in the slicing step, the heat-treated Cu-Ga alloy ingot 81 is cut with a diamond band saw device 1 or a multi-wire saw device 10 in such a manner that a cut surface is perpendicular to the shortest side of the rectangular parallelepiped shape.