Child safety seat

A child safety seat includes a backrest; a headrest formed with a shoulder belt hole; and a shoulder belt extending through the shoulder belt holes, wherein a back surface of the headrest has a first connector and a front surface of the backrest has a second connector, and the first connector is attached to the second connector in a height adjustable manner. The child safety seat may synchronously adjust the height of the shoulder belt while adjusting the height of the headrest.