PURPOSE: To provide a resonator installing device which has an excellent installing workability, and can confirm the installing condition easily.

CONSTITUTION: A shoulder bolt 11 is inserted to a resonator 1 made of a resin by inserting its head, the shaft 11b of the shoulder bolt 11 is inserted to a side panel 2 so as to position the screw 11c of the shoulder bolt 11 to an engine room 13 side, and a nut 15 with washer is screwed to the screw 11c, so as to install the resonator 1 to the side panel 2. The screwing of the nut 15 with washer to the screw 11c can be carried out at the engine room 13 side, and the fastening work is made easier. And by positioning the connection of the screw 11c and the nut 15 with washer at the engine room 13 side, the connection can be observed visually, and the screwed condition can be confirmed easily after the installing work is finished.