A handling device for handling drill string components (8, 8′,8″) in a rock drilling rig (1), wherein the handling device includes a gripper unit (11) for gripping drill string components (8, 8′,8″) to be put into and be brought out from the rock drilling rig, and wherein the gripper unit (11) includes grippers (12,13,14) operational for gripping components positioned in a gripping position, which defines a grip position axis (G). The gripper unit (11) is supported swingable between: a) a first position, wherein the gripper unit is positioned for engagement with an end portion of a first drill string component (8′) and an end portion of a second drill string component (8″) in and aligned with said active drill string position (A), and b) a second position, wherein a gripper unit (11) is positioned for engagement with an end portion of a drill string component in a delivering position for drill string components that are to be brought into respectively taken away from said active drill string position (A). The invention also concerns a rock drilling rig and a method.