The present invention relates to a prefabricated reservoir reinforcement device in an apartment house to reinforce a joint between a tie rod and an assembly panel inside a reservoir, comprising : a support piece (31a, 31b) formed on a rod bracket (30) to support a panel flange (22p) in one side; a bent piece (33a, 33b) to form a gap (32a, 32b) between the top and the bottom of the rod bracket (30) to allow the panel flange (22p, 24p) to be inserted; an engaging piece (34a, 34b, 35a, 35b) to restrict the insertion depth of the panel flange (22p, 24p) into the gap (32a, 32b); a burring part (36) formed on one side of the rod bracket (30) and having a tap hole (36t); a clamp bolt (37) to pressurize the panel flange (22p, 24p) into the support piece (31a, 31b); a pair of solid shafts (40, 50) placed between an assembly panel (22, 24) and a wing part (38, 39); a sealing part (42, 52) separately inserted into a sealing groove (41, 51); a release boss (43, 53) formed at an end of the solid shafts (40, 50); a release hole (38h, 39) formed on the wing part (38, 39); a stud bolt (44, 45, 54, 55) separately joined to the wing part (38, 39) and the assembly panel (22, 24); and a ring magnet (66, 68) to absorb the solid shafts (40, 50) using magnetism.COPYRIGHT KIPO 2015