To efficiently and easily carry out detachment work of a ventilation part of a decorative cover body sometimes becoming a hinderance depending on construction conditions of a flexible long object such as a coolant pipe or a ventilation hose, in one flow without removing the decorative cover body.

In the decorative cover body A fixed to an outer wall surface in a state covering a bent part of the flexible long object 1 led out through a through hole of a wall body in an attitude hugging the outer wall surface 2a, the ventilation part 6 provided with a multiplicity of ventilation holes 6a is formed on a ceiling wall part 5A facing the through hole, a ventilation cover 7 forming a ventilation passage for communicating the ventilation holes 6a and the exterior is detachably provided on an outer face of the ceiling wall part 5A of the decorative cover body A, the ventilation part 6 is composed such that it is detachable from an exterior side with respect to a ventilation opening part formed on the ceiling wall part 5A of the decorative cover body A, and an attachment maintaining means B is provided for maintaining the ventilation part in an attached attitude.