Provided is a highly versatile attachment component corresponding to a space around an attachment location of a vehicular member. A retainer for attaching an ultrasonic sensor to a vehicle has a member holding portion for holding the ultrasonic sensor; and an attachment portion that is to be attached to the vehicle. The attachment portion has a center attachment part; a plurality of attachment pieces which are an upper attachment piece, a lower attachment piece, a left attachment piece and a right attachment piece; and cuttable sections joining the center attachment part and the multiple attachment pieces. These attachment pieces can be removed by cutting the cuttable sections. Therefore, some of the attachment pieces may be removed so as to secure a space around a location to which the ultrasonic sensor is to be attached, thus allowing the ultrasonic sensor to be attached to the vehicle.