PURPOSE: To enhance further the sound effect of a vibrater, by forming a resonance box between a finish member and a car body panel.

CONSTITUTION: The forward part of a rear parcel cover 2 is detachable to the finish member 6 and is supported by an anchoring member 26 and a member 23 to be anchored, generally a gripping part 27 firmly holds an engaging bar 21 and is rigidly supported, and the rear part is forced against to a stepped part 64 of the finish member 6 via a resilient body 34 by a back door B. The low sound vibrations generated by the vibrater 3 are transmitted from a rear parcel trim 2 to the resonance box formed between the finish member 6 and the car body panel 4 to cause it to resonate, and their enhanced vibrations are transmitted via sound outlets 67, 67... into the room to increase the sound effect.