To hardly fall by adhere-fixing this strut in the state of sponge to the center part of a coaster base paper with adhesive and sticking one side of a both face adhesive tape to the upper face of this strut in the state of sponge so as to increase the area of the bottom part of a light-weight glass.

A strut 3 in the state of sponge is adhere-fixed to the center part of the coaster base paper 1 in various shapes and with colors with an adhesive 2. The height of this strut 3 is made coincident with a height from the lowest part edge of the light-weight glass to use to its bottom surface and one side of the both face adhesive tape 4 is adhered to the top surface of the strut 3. Otherwise, one side of a circular both-face adhesive tape of a width to which the lowest part edge of the light-weight glass can be adhered is adhered to the center part of the base paper 1 in various shapes and with colors. At the time of using, the tape 4 or the circular both face adhesive tape of the coaster is removed to be adhered to the bottom face center part or the lowest part edge of the light-weight glass to make it difficult to fall the light- weight glass.