To provide a cap opener which does not damage a bottle mouth regardless of whether the user of the cap opener uses a normal cap opening operation method or a reverse cap opening operation method.

The cap opener 1 has tapered engaging claws 4 formed at the inner peripheral edges of the front end and the rear end of an opening, and each engaging claw is provided with protrusions and recesses 7 located outward of opposite ends in the circumferential direction of the engaging claw. In cap opening operation, the protrusions and recesses make contact with the top surface or peripheral wall of the bottle cap to prevent the cap opener 1 from moving in the direction to the bottle, which prevents damage to the bottle mouth.