The invention relates to a well tool assembly (1) comprising a setting tool (10) and a plugging tool (20). The plugging tool (20) comprises: an inner mandrel device (21) and an outer housing device (26), an upper sealing device (30), a slips device (40), a lower sealing device (50) and a centralizing device (60) connected to each other in an axial direction outside of the mandrel device 21. The slips device (40) is provided axially between the upper and lower sealing devices (30, 50). The centralizing device (60) is provided below the lower sealing device (50) or above the upper sealing device (30). When the centralizing device (60) is provided below the lower sealing device (50), the upper sealing device (30), the slips device (40), the lower sealing device (50) and the upper section (61) of the centralizing device (60) are axially displaceable downwardly and upwardly in relation to the mandrel device (21) and the upper section (31) of the upper sealing device (30) is connected to the outer housing device (26) and the lower section (62) of the centralizing device (60) is fixed to the inner mandrel device (21). When the centralizing device (60) is provided above the upper sealing device (30), the centralizing device (60), the upper sealing device (30), the slips device (40) and the upper section (51) of the lower sealing device (50) are axially displaceable downwardly and upwardly in relation to the mandrel device (21) and the upper section (61) of the centralizing device (60) is connected to the outer housing device (26) and the lower section (52) of the lower sealing device (50) is fixed to the inner mandrel device (21).