A reinforcing body is disposed in a closed cross sectional portion constituted by one or more vehicle body components. The reinforcing body is provided with a joining portion to be joined to the vehicle body components. The joining portion includes hard connecting portions connected to the vehicle body components in an abutting state, and a soft connecting portion connected to the vehicle body components via a vibration damping member. The storage shear rigidity (KB′) of the vibration damping member is set in the range: 800 N/mm