To provide the adapter attached to the spout of a spouted pouch so as not to be loosened from the spout.

The adapter 1 is an adapter constituted so as to connect the spout 7 of the spouted pouch 10 and a tube member and has a connection part 2 for connecting the tube member and an attaching part 3 rotated in a clamping direction to be threaded with the spout 7. A baffle means for regulating rotation in a loosening direction is provided to the attaching part 3.