To efficiently carry out installation work on a vehicle body including a suspension spring.

The suspension spring 30 is arranged between a lower arm 10 held on a suspension cross member 1 and the vehicle body. A plate 20 for assembling is integrated with the suspension cross member 1. The suspension spring 30 is arranged and held between the plate 20 for assembling and the lower arm 10 in a state that a spring seat 31 contacts with the plate 20 for assembling from below in before the suspension cross member 1 is mounted on the vehicle body. The spring seat 31 is pressurized downward by the vehicle body 40, and the spring seat 31 is separated L from the plate 20 for assembling in a state that the suspension cross member 1 is mounted on the vehicle body.