CHILD SEAT SUPPORT DEVICE

A child seat support device that eliminates a need for an adjustment of a length of a support device by a person in charge of mounting of a child seat to ensure an improvement in safety is provided. A support device (10) for a child seat (50) is placed on a seat cushion of a vehicle seat and fixed to the vehicle seat. The support device (10) includes a fixed portion (12) fixed to the child seat (50) and a movable portion (14) supported via the fixed portion (12). The movable portion (14) extends to a vehicle floor. The movable portion (14) includes an automatic adjustment mechanism and a lock mechanism. The automatic adjustment mechanism changes a length of the movable portion (14) from the fixed portion (12) according to a height of the vehicle floor to bring a lower end portion of the movable portion (14) into abutment with the vehicle floor. The lock mechanism stops an operation of the automatic adjustment mechanism in association with a change in acceleration of a vehicle.