An assembling construction assembles a mountable member to a support member by holding a head portion of a clip on a mounting seat of the mountable member while securely fitting a leg portion in a mounting hole in the support member, the mounting seat has an instruction groove and guide grooves, the head portion of the clip has a first flange portion beam-like strip-shaped elastic pieces and which are brought into press contact with end portions of the guide grooves and stopper projections which are adapted to be brought into engagement with the end portions of the guide grooves when the clip is attempted to be shifted largely relative to the mounting seat.