To obtain sufficient rigidity against vibration even when an engine mount is directly installed on a cross member.

This engine mount installation structure for a cross member 5 with a box sectional shape has a connecting flange portions 5a, 5b at both of the front and rear ends thereof. In the structure, left and right connecting portions 11, 12 which contact the top surface of the cross member 5 with an adequate distance in left and right from the cross member 5, and front and rear connecting portions 13, 14 that contact the top surface of the front and rear connecting flange portions 5a, 5b are provided. The left and right connecting portions 11, 12 are fixed by tightening with bolts 21, 22 which penetrate the cross member 5. The front and rear connecting portions 13, 14 are fixed by tightening with bolts 23, 24 which pemetrate the connecting flange portions 5a, 5b.