An identical engagement hole 12b is formed in each of first and second brackets 1, 2. A first engagement portion 31c is formed in a damper body 31 of a rotary damper 3. A distal end portion of a rotor 32 of the rotary damper 3 is non-rotatably inserted in an adapter 4. A third engagement portion 46 is formed in an outer circumference of the adapter 4. The first engagement portion 31c is non-rotatably inserted in the engagement hole 12b of the first bracket 1. The third engagement portion 46 is non-rotatably inserted in the engagement hole 12b of the second bracket 2.