An adjusting mechanism adjusts a boat to be parallel to a furnace having an opening and a receiving space, which has a first symmetrical line. When the boat having a second symmetrical line is inserted into the space, a first gap area is formed between sidewalls of the space and the boat. The mechanism includes an adjusting element and an adjusting tool, which is removably disposed in the opening and has a wide part, a narrow part and a through hole. The narrow part blocks the opening. When the boat is inserted into the space, a second gap area smaller than the first gap area is formed between the sidewalls of the boat and the through hole at the narrow part. The adjusting element adjusts the first and second symmetrical lines to be parallel to each other according to the second gap area.