A child seat is provided which can ensure to stop a seat plate at a desired level and which can easily allow the adjustment of the height of the seat plate. The seat plate having a front seat plate and a rear seat plate is supported to a seat body having a seat back such that the seat plate can be moved up and down. The seat plate is supported by front links and rear links. By moving backward or front ward a slide frame disposed on a lower surface of the seat plate, pins are guided by guide slits formed obliquely so that the pins advance or retreat to be in or out insertion holes.