Abstract: An apparatus for booms, preferably so-called self-expanding booms, which includes a plate arranged on a platform, which plate is rotatable by a motor unit. The apparatus also includes a winder for winding up the boom. The winder is placed in the middle of the plate. A feeder for feeding-in the boom is arranged at an outer portion of the platform. The platform and the motor unit feeder are designed in that way that the later ones can be plugged into and out from the platform. The plate is designed in that way that it can be driven by a gear pinion which is arranged in the motor unit, and which goes into engagement with the plate when the motor unit is plugged into the platform. The feeder is designed and positioned in that way that the boom can be pressed togetherto a compact package when the boom is pulled-in, without need of extra guiding rolls.