To provide a cap fitter that improves serviceability by fitting a funnel-shaped cap to a zippered bag.

The cap fitter C includes a zipper part at the mouth of a bag made of film for opening and closing the bag. The zipper part includes a zippered bag 1 comprising a projecting member 11a and a recessed member 11b that can fit each other, a cap 2 open at front and rear ends, a substantially semicircular cap side projecting member provided on the outside of the cap 2, and an substantially semicircular cap side recessed member provided on the outside of the cap 2. The cap side projecting member fits into the recessed member 11b and the projecting member 11a fits into the cap side recessed member.