A platform unit used with a scaffolding structure includes a worker's platform and a ladder for climbing onto the worker's platform. The platform unit includes a first tipping prevention member adapted to interact with a substantially horizontal longitudinally extending first support member, and a second tipping prevention member adapted to interact from below with a substantially horizontal longitudinally extending second support member. The second support member is vertically spaced apart from the first support member. At least a part of at least one of the first and second tipping prevention members is vertically adjustable for enabling attachment and detachment of the platform unit to the scaffolding structure. At least three rollers support the platform unit, with each of the rollers adapted to rest against either the first support member or the second support member, such that the platform unit is rollingly movable in the longitudinal direction.