To provide a hole punching device for a cap of a compact bottle, and to provide a cap of a PET bottle having a hole formed by the hole punching device for the cap of the PET bottle.

A turning base 17 is turned in a clockwise direction in a horizontal plane until a side plate 19 abuts on a stopper 65, thereby the turning base 17 evacuates from the upper side of a support portion 9, and is brought into an open posture where the upper side of the support portion 9 is opened. In the state where the turning base 17 is brought into the open posture like the above, a cap 93 is put on the support portion 9 from the upper side. The cap 93 is supported in a state where a top plate 95 is mounted on the support portion 9. In the open posture, the turning base 17 is brought into a state having largely evacuated from the upper side of the support portion 9, and the upper side of the support portion 9 is completely opened. Accordingly, the cap 93 can be easily put on the support portion 9.