To provide a child seat for a two-wheeler, positively and easily ensuring the safety of a child even in case of the occurrence of a collision.

When forward inertia force is applied to this child seat for the two-wheeler due to the collision, shear pins 12 are broken by the force applied to a connection part 11 through arms 5 to release connection between the connection part 11 and a casing of an energy absorbing part 6. Rewinding force is thereby generated to a steel strip 8 connected to the connection part 11, and the steel strip 8 is rewound while rotating a rotary shaft 10. At this time, the energy of the inertia force is absorbed by plastic deforming force required for rewinding the steel strip 8. When the steel strip is rewound in the total quantity, the child seat for the two-wheeler is completely free from the restriction of the two-wheeler 1 and released into space. At this time, since the inertia energy of the child seat for the two-wheeler is lost, the child seat is prevented from jumping out forward with force, thus ensuring the safety of the child.