Rotation device, which includes a structure and a direct-drive pressure-medium operated turning device attached to the structure coaxially relative to the axis of rotation, wherein the structure of a rotation device includes - suspension means for suspending the structure of the rotation device from a boom, - a first inner body part comprising first conduits fitted to the first inner body part for leading a pressure medium through the first inner body part, - a second outer body part, arranged at least partly around the first inner body part completely rotatably, comprising connections fitted to the second outer body part for leading the pressure medium through the second outer body part, - second conduits fitted to either the outer surface belonging to the first inner body part or to the inner surface belonging to the second outer body part or to both for leading the pressure medium in all the mutual attitudes of the first inner body part and the second outer body part from the first conduit to the said connections, - an axial conduit for leading electrical conductors through the first inner body part and comprising two ends (16.1, 16.2), - bearing means arranged to permit the second outer body part to rotate relative to the first inner body part and vice versa, which bearing means are arranged to carry loads both axially and radially, - attachment means for attaching a direct-drive pressure-medium operated turning device to the structure coaxially relative to the axis of rotation between the first inner body part and the second outer body part in order to transmit torque, in which structure there is an axial conduit extending from the suspension means through the structure and the turning device attached to it for carrying electric conductors, characterized in that the rotation device further includes an adapter for permitting the complete rotation of electric conductors, attached to a under-surface belonging to the turning device in operating attitude of the rotation device, and the turning device is attached, in the operating attitude of the rotation device, underneath the second outer body part, to a second under-surface belonging to the second outer body part. - suspension means for suspending the structure of the rotation device from a boom, - a first inner body part comprising first conduits fitted to the first inner body part for leading a pressure medium through the first inner body part, - a second outer body part, arranged at least partly around the first inner body part completely rotatably, comprising connections fitted to the second outer body part for leading the pressure medium through the second outer body part, - second conduits fitted to either the outer surface belonging to the first inner body part or to the inner surface belonging to the second outer body part or to both for leading the pressure medium in all the mutual attitudes of the first inner body part and the second outer body part from the first conduit to the said connections, - an axial conduit for leading electrical conductors through the first inner body part and comprising two ends (16.1, 16.2), - bearing means arranged to permit the second outer body part to rotate relative to the first inner body part and vice versa, which bearing means are arranged to carry loads both axially and radially, - attachment means for attaching a direct-drive pressure-medium operated turning device to the structure coaxially relative to the axis of rotation between the first inner body part and the second outer body part in order to transmit torque,