A child seat for a vehicle which can be firmly secured to a vehicle seat even with a shoulder belt of a three-point seat belt and which can wind up the seat belt to securely apply a predetermined tension to the seat belt. The child seat includes a child seat and a shaft attached to the child seat. The shaft is rotatable about an axis of the shaft. Additionally, a first end of the shaft is disposed at a higher elevation than a second end of the shaft. The shaft further includes at least one slit configured to accept a seat belt.