A method for manufacturing an automobile, comprising: placing a body on a pre-assembled underside part set, and then assembling the underside part set onto the body, wherein the underside part set includes a rear suspension in which a spring and a shock absorber are arranged side by side, and characterized by bringing the spring into a compressed state in the underside part set before placing the body on the underside part set, wherein compressing the spring comprises: inserting a threaded shaft of a compression jig through a spring seat included in the rear suspension, the spring being placed on the spring seat, attaching a conical upper pressing plate of the compression jig at the middle of the spring and detachably engaging an opening formed in a central part of the upper pressing plate with an upper end of the threaded shaft, a part of the upper pressing plate being cut out so that the cut-out part has a fan shape extending from the opening, putting a lower pressing plate of the compression jig on the threaded shaft from a lower end thereof, and screwing a nut on the threaded shaft from an underside of the lower pressing plate so that the lower pressing plate presses the spring seat from an underside thereof, and the spring is compressed between the upper pressing plate and the spring seat. placing a body on a pre-assembled underside part set, and then assembling the underside part set onto the body, wherein the underside part set includes a rear suspension in which a spring and a shock absorber are arranged side by side, and characterized by bringing the spring into a compressed state in the underside part set before placing the body on the underside part set, wherein compressing the spring comprises: inserting a threaded shaft of a compression jig through a spring seat included in the rear suspension, the spring being placed on the spring seat, attaching a conical upper pressing plate of the compression jig at the middle of the spring and detachably engaging an opening formed in a central part of the upper pressing plate with an upper end of the threaded shaft, a part of the upper pressing plate being cut out so that the cut-out part has a fan shape extending from the opening, putting a lower pressing plate of the compression jig on the threaded shaft from a lower end thereof, and screwing a nut on the threaded shaft from an underside of the lower pressing plate so that the lower pressing plate presses the spring seat from an underside thereof, and the spring is compressed between the upper pressing plate and the spring seat. inserting a threaded shaft of a compression jig through a spring seat included in the rear suspension, the spring being placed on the spring seat, attaching a conical upper pressing plate of the compression jig at the middle of the spring and detachably engaging an opening formed in a central part of the upper pressing plate with an upper end of the threaded shaft, a part of the upper pressing plate being cut out so that the cut-out part has a fan shape extending from the opening, putting a lower pressing plate of the compression jig on the threaded shaft from a lower end thereof, and screwing a nut on the threaded shaft from an underside of the lower pressing plate so that the lower pressing plate presses the spring seat from an underside thereof, and the spring is compressed between the upper pressing plate and the spring seat.