To provide an improved safety seat for an infant, a child or an elderly person capable of preventing the danger with the optimal getting-on posture while utilizing the impact force when an impact is applied to a car body.

This means moves a seat for infant, child and elderly person, which has the structure that a seat and a back rest to be placed on a seat inside of a cabin can be freely slid, forward and backward when an impact is applied while removing a fixing means of a sliding part with the impact force so as to avoid the danger of impact.