Differential gear case and method for processing same

A differential gear case comprising:

• a container housing of a differential gear, the container housing having on an outer surface thereof an annular flange that extends around an axis of rotation of the container housing, and one of two areas of the container housing that are separated by the annular flange being formed with an opening that is communicated with a containing space formed in the container housing,
• in which:
• the area of the container housing that is formed with the opening is provided with a fixing portion that is used for fixing the differential gear case, and
• the fixing portion comprises two flat surfaces that are in parallel with a plane surface containing the axis of rotation of the container housing and arranged around the axis of rotation keeping a space therebetween,
• wherein an edge portion bordering the opening has, at an outside edge portion of a side that substantially parallels the annular flange, the fixing portion that is integral with the edge portion, and wherein the fixing portion has a rectangular cross section that includes the two flat surfaces and a flat upper end surface that extends between the two flat surfaces;
• and in which the fixing portion includes two flat raised portions, each arranged at outside ends of the outside edge portion and integral with the two flat surfaces.