Abstract: A vehicle body assembling line includes a door installing station where vehicle side doors are installed on the body. In the installing station, there is an installing robot which is planned to operate in a predetermined sequence to install the doors on the vehicle body. For supplying appropriate doors to the installing robot from the door storing sections, a door pick up mechanism is provided to pick up an appropriate door from the storing section and a door transferring carriage is provided to receive the door from the pick up mechanism and transfer to the robot. The arrangement can afford an effective door installing operation.