An insulating spacer 30 comprises a plurality of unit spacers 40, and a flexible
coupling portion 41 for
coupling the unit spacers 40 along the axial direction thereof, wherein the unit spacer 40 comprises a plurality of annular plates 42 and 43 each having an
insertion hole 44 for inserting the auxiliary
anode 11, and a
coupling frame 45 for coupling the annular plates 42 and 43 in the axial direction of the auxiliary
anode 11 while opening the outer circumference side thereof. The auxiliary
anode unit 10 is constituted by inserting the insulating spacer 30 into the auxiliary anode 11, and since each unit spacer 40 is coupled, the distal end of the auxiliary anode 11 is naturally located in proximity to the
insertion hole 44 provided in the next unit spacer 40 when the auxiliary anode 11 penetrates one unit spacer 40. Accordingly, the auxiliary anode 11 can be inserted into the insulating spacer 30 by series of works, and as a result, the auxiliary anode unit 10 can be manufactured with good workability.