To obtain a method of attaching a cap to a PET bottle which makes it easy to remove a tamper evident band from a bottle mouth after opening and which prevents the deformation of the band when it is initially screwed on.

The plastic cap 6 is provided with a cap body 7 with a female threading 7a on its inside periphery, an annular tamper-evident band 8 whose circumference keeps a longitudinal slit 8b or a cut partially bored and inside periphery many catching pieces 8c protruding in the axis center direction are formed and many bridge parts 9 connecting the band to the bottom of the body. A mounting jig 10 is tightly fitted to the outer periphery of the cap body and the outer periphery of the band, the cap is rotated through the jig for screwing the cap body on the mouth 3 of a PET bottle 1 and the band is fitted and caught on the flange 5 of the mouth of the bottle.