An agitator tool (1) for introducing forward and backward axial movement in a downhole tool of a drill string, where the agitator tool has a first axially moveable element (5) coupled to a second laterally moveable element (9) arranged inside a housing (2) via mechanical coupling. The mechanical coupling may be a pin and groove arrangement where the groove forms a modified or unmodified sinus shaped guiding loop that allows the first element (5) to oscillate within the housing (2). The second element (9) is driven by a turbine unit which may have flow regulating means. This provides an agitator tool comprising with very few moving and wearable parts. The shape of the groove sections allows an accelerated and/or de-accelerated forward and backward movement of the first element (5) that allows it to be used for various applications in a bore hole.