A control apparatus includes a body, a fixation plate and a control circuit arrangement. The body includes first and second fluid passages, which conduct fluid. The fixation plate is installed to the body on one side of the body and includes a third fluid passage, which has a first end connected to the first fluid passage and a second end connected to the second fluid passage. The third fluid passage conducts the fluid from the first fluid passage to the second fluid passage. The control circuit arrangement includes a board and a plurality of on-board devices. The board is installed to a surface of the fixation plate, which is located on one side of the fixation plate that is opposite from the body. The on-board devices are arranged on one side of the board, which is opposite from the fixation plate.