To provide a coaster for absorbing droplets dripping from a container without wiping every time a table or clothes wetted by the droplets dripping from the container containing a cold beverage when an air temperature is high.

For a coaster, a rubber band is attached to the opening of a water absorbing bag, it is put on the bottom of a container and is made attachable and detachable to/from a container of any bottom shape, and a table and clothes are prevented from getting wet by droplets of the container containing a cold beverage.