Abstract: A child seat has an upper base section (1) and a lower base section (201) for changing an inclination angle between these base sections. The upper base section 1 and the lower base section (201) are journaled rotatably about a common journal axis (201A) at the front portion of the base. At a rear end side, an inclination angle changing mechanism (200) is installed for adjusting a spacing between the upper base section (1) and the lower base section (201) opposite the journal axis (201A). This structure provides a child seat allowing adjustment of the angle of inclination of a support surface supporting a child even if the child supporting surface extends lengthwise of a passenger car seat to which the base formed by the two base sections 1 and 201, is attached. This leveling of the child supporting surface is possible if the child seat (2) is rotatable about a vertical axis relative to its base.