A rotation device (12) for rotation of equipment (13) fastened at the region of a distal end of a boom (9,11), which has a general longitudinal axis, and which is part of a boom device (3) which is fastenable to a carrier (2) for a mining or constructions work rig, wherein the rotation device includes a first rotation unit (Rl) arranged to rotate the equipment around an axis (Al) which is essentially parallel to the longitudinal axis of the boom and a second rotation unit (R2) which is arranged to rotate the equipment around an axis (A2), which forms an angle with the longitudinal axis of the boom. The rotation units (Rl, R2) are fastened to an angle unit (12'), which is included in the rotation device (12) and has rotational axes (Al, 21; A2,22) extending at an angle with respect to each other, and are connectable to the boom (9,11) as well as to said equipment (13) . The invention also concerns a mining or constructions work rig and a boom.