The present disclosure provides a retaining device for a carrier, which includes a base support assembly connected to and supporting a base of the carrier, a retaining assembly configured to secure the carrier to a vehicle seat, a fastening rod provided on and movable with the base support assembly, a slider provided within the retaining assembly and engaged with the fastening rod such that the fastening rod is able to move the slider, and a cushioning assembly engaged with the slider. The cushioning assembly provides cushioning to the slider when an impact force from the slider applied to the cushioning assembly reaches a predetermined value, allowing for a movement of the slider from a first position to a second position.