To manufacture a viscoelastic damper easily at low cost.

A material that is solid at room temperature and shows a molten state when heated is used as a viscoelastic material 4. The visoelastic material in solid form is sandwiched between steel plates (plate members) 3, is melted by heating from outside the steel plates, and re-hardened through cooling. The steel plates are laid flat, pellets of viscoelastic material are laid over their upper surfaces, other steel plates are laid flat thereon, and after the steel plates are assembled together, they are entirely stood and heated. A heat-resistant sealant 7 is attached to three sides of the peripheral edge of each steel plate and the viscoelastic material is filled inside the sealant. While the steel plates are temporarily fastened together by means of assembling bolts to restrain their displacement in a mutually separating direction, displacement of the steel plates in a mutually approaching direction is permitted by means of collar members.